One would expect the author to explain that. But we are talking about Nicholas Farrell, who is not very good at history.

I am assuming he didn't cover the historiographical debate surrounding Italy's foreign policy during the 1930s - and especially the relations with the Western Powers leading to Italy's alignment with Germany after 1936.

That Italy wanted to ally with France and Great Britain is quite dubious a claim. Italy had more or less consistently appealed to the idea of a "revision" of the Treaties since the early 1920s. What this "revision" actually entailed tended to vary from one voice to the other, and Italy didn't pursue - for very obvious reasons - a break-up with the British and French. The perspective of "adjustments" being made to an "unfair" European order was nonetheless a portion of Italy's diplomatic and political discourse, a leverage of sorts both to place Italy on a stronger diplomatic ground compared to those nations that were more invested in the mainenance of a political and economical status quo, and an instrument of penetration into neighboring European countries that included supporting local groups in order to maintain a certain degree of political instability. The results of these policies were "mixed", even from the perspective of the Regime, and certainly didn't contribute to increase its dependability reputation.

So, while Italy tended to react with a degree of genuine alarm at the swift rise of Hitler and subsequent power vacuum - a potential sign of major instability directly encroaching on Italian positions, as testified by the perceived aggression on the Austrian independence - it also didn't renounce to its action of destabilization. So, while Italy sought to prevent the anschluss, it also became involved with the assassination of King Alexander of Yugoslavia and French foreign minister Barthou - the latter an incident, but certainly not encouraging a trusting attitude.

While I am not particularly versed in the diplomatic history of France and Great Britain, I think it's fair to say that neither of the two nations saw Fascist Italy as a trustworthy diplomatic partner already in the build up to the invasion of Ethiopia. Italy tended to appear as a source of instability, and thus Mussolini's openings were often seen as duplicitous.

That's not a particularly odd situation in the diplomatic world and I tend to concur that - broadly speaking - Italy continued to pursue somewhat conservative diplomatic directions (or, at least, consistent with pre-Fascist foreign policies) even by the latest stages of the build up to WW2. These structural goals were nonetheless pursued with a greater degree of ideological aggressiveness and with limited concern for the impact of those initiatives so that the Regime, willingly or unwillingly, laid the ground of its political isolation.

At which point, the answer to your question is that - in essence - the British and French didn't see Italy as a viable partner to ensure the European stability because they didn't trust it. And, yes, the fact that they proved more willing to appease Germany - for a while, and obviously accounting for the fact that German diplomatic "revisionism" could be much more impactful than Italian one - than to come to favorable terms with Italy speaks a lot of Italy's diplomatic failures.

Even then, there certainly were portions of the British and French diplomacy and political leadership that believed that an accommodation with Italy could be found at a lesser cost than suffering the consequences of its alignment with Germany - the Laval-Hoare pact is an example, albeit ambiguous, of these tendencies.

On these points, I'd say that historiographical interpretations tend to be consistent. A divergence tends to occur with regards to the subsequent developments taking place after Italy's invasion of Ethiopia. The "intentionalists" - led by Knox - tend to stress the elements of consistency in this foreign policy, leading to and continuing after the Ethiopian war, building a picture of Italy's actively working to undermine what might have been otherwise a manageable European balance. Italian historians - not only those following De Felice - tend to see these foreign initiatives as a reflection of Italy's internal matters, economical struggles and possibly loss of popular support; and therefore are led to present a picture in which the Italian aggressiveness was largely a reflection of "posturing" and where large portions of the establishment were actually seeking, and would have been open to an eventual accommodation with the Western powers.

I do believe that both groups tend, at times, to overstate their case (especially when arguing with each other). It may not come as a surprise that diplomatic and military historians tend to ascribe particular importance to those sectors of the establishment as driving forces of a nation's overall foreign policy; while political and economical historians tend to read the latter as an expression of internal issues and financial situations. Both groups also have a point: I agree that Knox for instance tends to overlook a whole lot of internal factors in driving the initiatives of the Italian Foreign Office and government; but he is correct in pointing out that most traditional interpretations of Italy's foreign policy and international relations tend to rely on a limited command of foreign sources and documentary evidence, and thus are inclined to present an overly fragmented version of it.

I hope this clears it up a bit.

There are quite a few biographies of Mussolini. I won't say that Farrell's one is the worst, because there are worse ones, but it's bad enough not to recommend it.

If one doesn't have the time to bother with De Felice, Pierre Milza's relatively recent one is accessible and quite balanced in its treatment of the matter.