A word of warning
I have been made aware of this thread and I'm concerned by the notion that someone is getting something for nothing.
Deadheading Duck, I'm sure your 'boffin accountant' would have explained to you that if you can legitimately claim a deduction as a business expense it merely reduces the amount of profit you make that would in turn be subject to tax. On the other hand, anybody can give away what they like provided it is not being done for the purpose of tax evasion. Please note the bold text.
The advice I have received, whilst not conclusive, would indicate that your 'sponsorship' would not be a legitimate tax deduction in the UK. Your 'donation' must be either a legitimate business expense (e.g. in staff training) or a donation to a registered charity.
Tax departments are not renown for philanthropic philosophies, especially if they can hook someone for tax evasion. The only thing you can be sure of is death and taxes. Sponsorship to help offset someone else's tax liability is a very iffy idea. Then of course, I'm not an accountant but I know a man who is!