my advice
would be to email your immediate supervisor basically saying what you've said here, and asking them to confirm that the policy is that you'll be fired if you go over budget.

Then when you have it in writing that

i) you've pointed out the problem, and
ii) you were told not to go over budget anyway

don't go over budget regardless of the consequences.

I'm not sure of employment law in Britain, but I assume there's some kind of redress in that situation.

Also my advice is not to take advice from people on b3ta.
(apeloverage committed the vile act of onanism on, Sun 25 Jan 2009, 9:15, Reply)