Iran wouldnt exactly be a walk over militarily, its a completely different ball game to Iraq, as in it actually has a decent air defence system something that Iraq was missing and made it very easy to get into, the Iranian army is also larger again. Iran is also one of the U.K's defence suppliers biggest customers, admittedly the stuff isnt as technically advanced as the US stuff but in the right hands i.e the U.K's its more than a match for most the equipment out their, however im not sure on the state of training that the whole iranian defence system would be in. Also im sure they have a fair bit of kit lying around from Russia and China so could all be used to a nasty mix.