In response to Foggy's comment about inheritance tax, the time lapse is 7 years from the date of transfer. If the person dies before 7 years are up then the property would be subject to inheritance tax.
Was not thinking about inheritance tax - but capital gains if at a later stage Carrie decides to sell the property
"Capital Gains Tax on property: the basics"
You usually don't have to pay Capital Gains Tax when you sell, give away, exchange or otherwise dispose of your own home. But you may have to pay Capital Gains Tax when you sell or dispose of a piece of land or a property that's not your main home.(HM revenue)
There is nothing illegal about these types of transfers - I have done the same with my own mother. I suggest that you wait until the IVA is over, at which time your son will be over 18 and legally entitled to own property. This is the excuse that you can give your Mum and Dad - and for the record the transaction can be overturned if they go into care within 7 years of the transfer.