No. Britain is perfectly capable of teaching Iran a lesson in the same manner as we did during the late 1980s (
http://en.wikipedia.org/wiki/Operation_Praying_Mantis), and should IMO but that's for another thread. It would require a much more concentrated effort than it did for the US, but the UK has a much smaller (but still very well trained and equipped military). It is a matter of willpower.
PD