The UK government has slashed incentives for charitable giving and this has caused tremendous concern amongst UK charities.  The UK government notes “… some individuals on very high incomes have used reliefs to pay little or no tax, sometimes year after year. This Government believes it is not right that taxpayers with very high incomes should, year on year, pay little or no tax as a result of unlimited reliefs.”  The government notes “Budget 2012 announced from 6 April 2013 there will be limits to the amount of income tax relief individuals can claim.  This cap will apply only to reliefs which are currently unlimited. This cap will be set at 25 per cent of income (or £50,000, whichever is greater).”

Here is a note from HM Revenue and HM Treasury:
http://www.hm-treasury.gov.uk/d/cap_unlimited_it_reliefs.pdf

Apparently many of the details have yet to be worked out.

A number of UK organizations have expressed concerns:

National Council for Voluntary Organisations (NCVO).
http://www.ncvo-vol.org.uk/news/civil-society/treasury-%E2%80%98buries-bad-news%E2%80%99-charity-tax

Charities Aid Foundation
https://www.cafonline.org/media-office/press-releases/2012/change-will-slash-donations.aspx