Can you legally use a CB radio whilst driving in the UK?

Yes you can, two way radios such as CB, amateur radio, taxi radio etc are exempt from the mobile phone laws. But be aware that you will be prosecuted if your use of a CB radio results in dangerous driving or an accident. Also, using one will give the police an excuse to pull you over much the same as they pull over vehicles that have blue LED lights which aren't illegal either. Have a look at the Police National Legal Database http://www.askthe.police.uk and do a search for CB or blue LED's but remember - the police just need an excuse to check both you and your vehicle.