Car seats in the UK - confused!

[allegretto]

My DS7 uses a booster with a back and my DD7 (but very tall) uses a booster without a back. My DS12 doesn't use a booster. We are in Italy where we are considered strange for even putting our seat belts on. We are visiting the UK this summer - is the above set up legal in the UK (especially booster seat without a back - DD didn't fit into hers anymore). Thanks!

How tall are your children?

They should be fine. Your 12 year old won't need a seat unless he is below 135 cm ( average height for a 9 year old). For the 7 year olds, a high back booster or a backless one should be fine.