Despite the negative publicity surrounding the practice during the MPís expenses scandal, flipping your private residence is still permissible.
Within two years of acquiring a second residence, e.g. a holiday home, it is possible to submit an election to HMRC to nominate the second property as your Principle Private Residence. After a period, which can be as short as a week, you can then alter the election back to the first property. The effect of this is that, for any property which at some time has been your private residence, the last 36 months of ownership are exempt.
Therefore if you keep the second property for just 3 years the sale will be free of capital gains tax. If you own it for longer a proportion of the gain will be exempt representing 3 years out of the total ownership.