Normally, UK legal CB radios are limited to just 4watts transmitted power, however it is very common to add linear ampilfiers which might increase the output to 100watts or even more, this is when you start to get problems with TVi
If its CB or radio related you will only get interference when the CB is transmitting, ie when the user is actually pressing the mic switch and talking. this obviously means you should see short irregular bursts of interference. If its much more regular say a pattern of five or ten seconds every few minutes, then its more likely to be caused by a paging transmitter or PMR system (private mobile radio,Taxis etc) As these radios, often transmit short regular bursts of data.
You can often cure TV interference by using a 4" Ferrite rod or a ferrite ring, simply wrap your tv aerial coax cable around it about ten times and tape it in place, about a metre from your tv. Of course if its affecting lots of people you need to get OFCOM to come and sort it out.