How in 1979 did a Mars Bar cost someone over £4,000 in prize money?

Hmm would this be something to do with someone eating a Mars bar before a competition and giving a reading for a banned substance. Excess caffiene or something.
I have a vague recollection about someone feeding a mars ba to a horse before a competion and the horse failed drug test but always thought that it was an urban legend.

Will try and search some more.

Or was it on the TV gameshow 'Lets Make A Deal' some guy opted for what was behind Curtain No. 2 instead of just taking the cash.

Gmack, Brinjal clearly gets the yay, but I did find a site (and only one) on this incident:

http://www.theanswerbank.co.uk/Sport/Question87630.html

I think Frankie and Brinjal should share the yay and a Mars Bar for that one.
As the site says, the horse No Bombs at Ascot won by eight lengths at Ascot but was disqualified when stimulants caffeine and theobromine were found in its blood test. These were traced back to a Mars Bar that was snatched from a stable boy on the way to the course and cost £4,064 in prize money.