You are right to suggest that the British government did not abolish slavery for wholly altruistic reasons; the extent to which it did so out of blatant self-interest though (in the sense that it had something to gain) is a more debatable.

The first thing to understand is that the economic world of 1833 was very different to the world of 1733; slavery in the British Caribbean was not the enormously profitable industry it had once been. After 1776, Britain's colonies had lost one of their major trading partners in the form of continental North America - the newly independent United States no longer needed to import goods exclusively from British suppliers. America was now an open market in which producers from the British Caribbean had to compete with their European, and even American, counterparts. Similarly, by 1833 the industrial revolution had well and truly matured; Britain's economy was awash with all kinds of new, innovative and highly profitable industry that had simply not existed a century before. The slave-driven agriculture of the Caribbean was no longer essential to the economic health of the British Empire as it once had been, and just like slave goods, the plantation economy now had to compete with other avenues for capital investment by private financiers.

This in turn had profound consequences for the political dynamics of the British Parliament on the slavery question. In a world where industrialists were now very much part of the affluent upper class in society, political ideas and the balance of power were changing. The industrial revolution had brought with it ideas about the merits of free trade and free labour; that competitive market economies would always provide the healthiest kind of society possible. Slavery was fundamentally opposed to these kind of ideas. Similarly, the power of the planter class as a parliamentary bloc was somewhat reduced, as MPs had alternative source of revenue or sponsorship and industrialists were themselves now entrenched as members of the political class.

After the Whigs were swept to power at the 1831 election, they had presided over one of the most dramatic pieces of electoral reform in British history - nearly all of the country's so called rotten boroughs (tiny constituencies with just a handful of voters, where whoever owned the land could effectively control the outcome of the election; one constituency had just a dozen voters electing 2 MPs!) were abolished and the franchise was extended to one-fifth of the wealthiest adult men. Sweeping boundary changes were introduced to make the system general fairer, though it was still imperfect, the new system is fundamentally the same as the one that still exists in the UK, and British historians will usually refer to the following 1832 election as the beginning of 'proper' British democracy in the modern sense of the word. The effect of these changes was a reduction in the influence of those who still had vested interests in the slave trade (many either saw their seats abolished or swept away in the Whig landslide) and the election of a whole slew of anti-slavery MPs.

The success of these MPs in being elected reflected the success of a long-standing anti-slavery campaign in the UK, which had mobilised public opinion against slavery effectively for decades. Abolition in 1833 represented the culmination of anti-slavery agitation. In 1807, the British government had relented to pressure to abolish the transatlantic slave trade, and taken the position that the slave trade was contrary to 'natural justice' - a position that implicitly suggested slavery was in itself immoral. The slave population in the British Caribbean had never been self-sustaining in the same way; its growth depended upon the continued import of new slaves from Africa. Without the trade, abolitionists had hoped to effectively force the planters into submission and abolition. Whilst this didn't happen - there is evidence the planters continued to import slaves from the Portuguese clandestinely, though not on the scale they required - it had been a huge blow to the sustainability and legitimacy of British slavery.

As it became apparent that the end of the slave trade was not doing much to alter the conditions of slavery in the immediate term, attention turned to the conditions in which slaves lived in the Caribbean instead. Outrage at how horrendous slavery could be led the British government to introduce measures for amelioration - new rules that were intended to protect slaves from abuse by their owners, including protecting families from breakup, outlawing flogging in the fields, local government regulation of punishment and a right to purchase freedom without consent of the owner. Unsurprisingly, these reforms were - to the anger of the British government - largely ignored by the planters and the colonial bureaucracy closely associated with them. Britain was, then, in something of a moral and political quandary. The Government had abolished the trade for its inhumanity and acquiesced to new regulations to protect slaves from abuse, yet slave-holders refused to implement them, suggesting that any reform should of abolition to improve conditions in the islands would ultimately be a failure.

Arguably the last straw for the British government came in 1831. On Christmas day, tens of thousands of slaves on the island of Jamaica rose up in a rebellion that appeared to have been disturbingly well-organised; led by a Baptist preacher Samuel Sharpe, the rioters had been demanding effective emancipation and wages for their work. It was ultimately ineffective, though it caused considerable property damage across the island. The local government responded with extreme brutality against slave person and property for even the most minor of offences. Back in Britain, news of the rebellion prompted both outrage at how needlessly brutal the planters had responded to the uprising, and fear that more revolts would follow if conditions did not improve. Though less profitable and significant to the economy than ever before, the British did not want to risk seeing a repeat of the Haitian revolution on their islands.

But contrary to popular belief, only the abolition of slavery as a legal institution came in 1833 - not emancipation. Only slave children and the elderly were completely freed. The 1833 act created a new system known as apprenticeship, in which ex-slaves remained the de facto property for their masters for a fixed period of time - they effectively became indentured servants instead. Under this new system, they were theoretically entitled to a much stricter range of rights and entitlements, and an independent judiciary was created to enforce the new measures this time (this system would prove wholly ineffective). As such, though slavery was ended, the British solution allowed the planter class to retain their forced workforce for several years - the rationale being that it would give the Caribbean economy time to adjust and time for the planters and ex-slaves to figure out a new system of social relations. As such, the fashion in which slavery was abolished was very much intended to minimise the risk of political or economic instability in the British colonies. Apprenticeship would ultimately be ended prematurely in 1838, after repeated investigations uncovered massive abuse of the apprenticed population on a scale every bit as awful as slavery.

Furthermore, the British government invested a small fortune - £20million (equivalent nearly to the UK's budget deficit today) - in a compensation scheme for the former slave owners. Slaves had been both capital and labour; in a slave economy, every slave is a highly liquid asset easily exchanged for cash. As such, the abolition of slavery meant that a huge sum of money had suddenly been wiped out of the British economy; compensation was intended to try and replenish this stock of lost cash, whilst at the same time providing the planters with funds to regear their operations to a free labour system post-apprenticeship. By compensating the planters in this fashion and not the slaves, the British Government was being pragmatic, but also effectively endorsing slavery as a legitimate system that had merely out-lived its time and place.

In short then, no, Britain did not abolish slavery for purely idealistic reasons. Indeed, the Government was slow and cautious in the process of abolition and had an uneasy time finding a way forward with the whole process. Abolition was ultimately facilitated by changing political and economic conditions that made support for slavery less palatable and less profitable; there was as much a surge in anti-slavery sentiment as there was an increase in apathy among the political class as the question of slavery became less and less significant to Britain's future. The enormous compensation package for slave-owners, several of who still sat in Parliament, certainly reflects a measure of pragmatic self-interest in how abolition came about. It would however be wrong to say that it was only self-interest that motivated abolition; certainly among British voters and many of their representatives there was an authentic and passionate desire for the end of slavery. Slavery itself was at odds with the free market ideology that increasingly permeated the Whig, and later the Conservative, parties. Similarly, the Government was repeatedly responsive - albeit cautiously so - to allegations of systematic abuse against slaves and ex-slaves, perhaps motivated by a certain paternal interest in their well-being as well as the fear of rebellion.