Why is the 1812 war against the United States often overlooked in British history?

Because for the UK it was a minor conflict compared to the Napoleonic wars that were happening at that time.

What was the consequences of the war?

For the UK, very little. Even for the US the "practical" after effects of the war (in terms of concessions and whatnot) were not that big. It did help settle some conflict about the territory around the Great Lakes. While the casus belli of the US were satisfied, that had everything to do with the end of the Napoleonic Wars, and very little to do with the War of 1812. The Treaty of Ghent that ended the war didn't even address those issues.

Growing up in England I never heard about the war and it never came up in history lessons.

Cheer up, it's not that well covered in the US either. Every school child learns that British impressment of American seamen was a reason for the war (that's true, but it's not the whole story), the bad guys (that's you) burned Washington D.C. (though they may omit that by British design it was only the government buildings), and that Francis Scott Key wrote the poem that was later set to music as our national anthem "The Star Spangled Banner" while watching British ships unsuccessfully attack Fort McHenry in Baltimore Harbor. They may or may not learn that militarily the war was a draw.

I suspect one of the reasons that it's not covered in more detail is that there are political aspects that are embarrassing, or at least ironic. The US declared war only five days before Parliament had addressed the most important American complaint, though neither side became aware of the others actions for weeks because trans-Atlantic communications were so slow. For the same reason, America's most famous military victory, the Battle of New Orleans, was fought after the treaty had been signed by both sides, and ratified by the UK (though before it could be ratified by the US). It's also interesting that the Democratic-Republican party, whose support was mostly in the South and West, promoted the war, while the other major party, the Federalists, whose support was in the Northeast and particularly New England, opposed it. The irony is that most of the maritime industry in the US at the time was in the Northeast, and it was maritime issues that were the casus belli. Hence the part of the country that was most affected by the issues was the most opposed to the war. Later in the war there was even talk in New England of succession from the Union, though how serious the talk was is subject to debate. The final irony is that after the war the Democratic-Republicans, who had promoted a war that had no positive effect and had needlessly endangered the country, became more popular while the Federalists, who had opposed the war, disappeared (though admittedly they were on the wane before the war).