Although a letter to your friendly tax office is the best (and cheapest, if not necessarily the quickest) way to find out, bealzebub is right. The expense must be incurred 'wholly, necessarily and exclusively in the performance of your duties'. Expenses incurred to put you in a position to do a job which you don't already have are not allowable.
And yes, you can claim for the previous six tax years - i.e. you have until 5 April 2009 to make a claim for the year to 5 April 2003. How you make these claims depends on whether you fill out a self assessment tax return or not. Once again, a letter to your tax office (usually noted on your P60) is the best way to start.
Incidentally, if you are a pro pilot and a UK tax payer you are entitled to a 'flat rate expense' (FRE) in your tax code to allow for the normal yearly job expenses. If you don't have it, or aren't sure, once again (and at the risk of repeating myself) drop your tax office a line and ask them to review your code. Tell them your National Insurance number, the full name of your employer, and how long you've been employed as a pilot.
Last edited by arandcee; 11th Oct 2008 at 15:41.