Is this not clear enough?https://www.gov.uk/child-car-seats-the- ... oster-seat
New regs are for new booster seats:
Since April 2016, The new regulations come into force on 1st March 2017– but they only apply to New models, so you can continue to use backless booster seats you already own.
Under the new law, backless booster cushions should only be bought for kids who are both more than 125cm (4ft 1in) tall, and weigh more than 22kg (3st 7lb).
I noticed <no name german suppermarket> were selling off booster seats this week - no doubt to beat the ban