The RAF in the Middle East was suffering from gaps in production between aircraft versions

In the summer and fall of 1941, there were production transitions taking place among aircraft models and there were gaps between the phaseout of older models and the new models coming into production. These are some examples:

The Hurricane I was disappearing, but the number of
Hurricane II's available was driven by needs in Britain, which kept numbers down.

The Tomahawk (P-40C) was relatively new to the Middle East, but it was being phased out in favor of the Kittyhawk (P-40D and P-40E). Teething problems were expected with the new type.

Fighter Command versions of the Beaufighter were contingent on adequate supplies of ground-control radar for guiding interception. The tradeoff was that the Coastal Command version would require more aircrew from Britain.

Production of the Martin 167F Maryland was ending, but the replacement aircraft, the Baltimore (A-30) was delayed. The RAF was forced to send every Blenheim IV that was available, so that the Middle East would have medium bombers. Thre were very few of these left. As soon as they were available, Douglas Boston III aircraft would be sent.

The Wellington I heavy bomber did not do well in the heat, so the Wellington II was developed, but they were slow coming into production.

Bristol Beaufort torpedo bombers were in use in Britain, but had not reached the Middle East. They would need to be drawn from Britain for the Middle East. They are not listed in the appendix in Vol.II of the Official History, so they must not have reached the Middle East, yet.

This is based on the account in Vol.II of the Official History.