Here's what Which have to say on the matter -
"Rear-facing seats
In Europe, children up to 13kg (around a year old) generally travel rearward-facing. But in Sweden, authorities recommend that children are kept rear facing until they are at least four years old, and all seats have to be fitted initially by a professional.
In the UK, rear-facing seats are hard to find in and seats don?t have to be professionally fitted.
Swedish research that compared injuries suffered in cars by children under five showed that once UK children change to forward-facing seats, Swedish children of the same age fare better in accidents.
In a front impact, rear-facing seats usually protect well. We know this from testing Group 0+ seats and from testing we?ve done on Swedish rearward-facing Group 1 seats. But we've also found the complexity of straps and brackets required to ensure the seat is secure in rear-impacts makes them much more complicated, and less likely to be installed correctly.
Unless all UK child car seats are installed by a qualified professional, as in Sweden, rearward-facing Group 1 seats are unlikely to become widespread."