Since a couple can have assets between them of £650k left after they both die without fear of HMRC requiring Inheritance Tax (IHT) to be paid, unless you have assets greater than that including the house, there is no particular reason on those grounds to transfer the house to your heirs now anyway.
Plenty of reasons why it won't work to avoid future IHT, as others have pointed out above, unless you stump up the market rent (and live for at least another 7 years).
Then there's the business about care home fees, which one person above has pointed out won't be burdened onto the State - you'd be regarded as having 'deprived yourselves of your assets'.
So, all-in-all, time to rethink the scheme perhaps.