Hi Rob.
Your official answer is here:
http://www.hlf.org.uk/ It's the 'Heritage Lottery Fund' which allocates money from the 'National Lottery'.
For discussion of how it works from the user point of view, have a search on the FP Forum under those terms.
The v.v. short answer is from funds raised from the self sheering sheep, money is avaliable for projects that match the criteria. However, quite rightly, the fund expect a) the applicant to come up with match funding of the same value (as a rule) so you can only effectively apply for 50% of the project cost and b) a sound, detailed plan and application.
Hope this helps!
Cheers