The war when/if it comes will have an effect on both US and UK economies. Both are on the brink of recession, the increased government borrowing will tip them over the edge, particularly if interest rates go up - which is a very likely scenario.
The only thing that has been keepin the UK economy bouyant the last few months is consumer spending - a large part fueled by people releasing equity from their over-inflated houses.
Gordon Brown has budgeted for about a billion of extra cash to pay for the war - I don't think this will be nearly enough thanks to the underfunding of the British military in recent years.
Also, don't forget that overheads for the airlines will be higher - oil prices and the cost of insurance will go up.
IMHO, War = increased Government borrowing = interest rate rise = recession = less people holidaying/travelling by air = not good news for the avaition industry.
However, lets not forget that one of the main reasons for invading Irag is for George Dubya to award lucrative deals to his Texan oil industry buddies once the war has been won. Once the Yanks have control of Iraq and its oil, prices will go down and the economies will breathe a sigh of relief, and hopefully things will get better. Thats if Moslem radicals don't go blowing up airliners, releasing chemical weapons/tactical nukes in retaliation.
It will be a very large can of worms which will be opened should world opinion not convince the Cowboy that escalating the 'War on Terrorism' by invading Iraq is a bad idea.