You can as much as you like to whom you like without any DIRECT tax implications. (i.e. gifts don't count as 'income' when HMRC are assessing Income Tax, and there's no such thing as 'gift tax').
However IF you were to die within 7 years of making the gift, all or part of the money (depending upon the period of time that had elapsed) could be counted towards the value of your estate when deciding if there was any liability for Inheritance Tax. IF the total value of your estate came to over £325,000 (or to whatever figure the threshold had risen to by the date of your death), there would be a liability for Inheritance Tax.
Rules here:
http://www.hmrc.gov.u...ey-property/index.htm
Chris