Depends on the honesty of the goon. He stands to make commission from this, so he could be tempted to forge your signature. If you didn't give him your name you should be OK. The BBC/Capita can't proceed against an anonymous person.

You could try [email protected] If they don't handle complaints they should give you the e-mail address of someone who does. Please note that this person was an employee of Capita Business Services ltd and has no more authority than the postman. You do not need to talk to him at all and I recommend you don't. You can order (not ask) him to leave the property. Likewise the threatening letters have no legal standing and can be ignored. The whole aim is to get you to incriminate yourself. Don't do it. The caution begins "You do not have to say anything ..." That's sound advice and you should say nothing. Anything "produced in evidence" will not be for your benefit, it will be for the prosecution's. "Silence is the ultimate weapon of power" (Charles de Gaulle).

As far as I know the only data stored on the SIM are contact numbers. Music, pictures, video and other data are stored in the 'phone's internal memory or extra memory card. Those data will remain in memory when the SIM is changed. To retain contact numbers simply copy them over into the 'phone memory before swapping the SIMs. You can then transfer them back to the new SIM. It might be an opportunity for a bit of a clean up of old contacts ... I got my first cellphone in August 1997 and have swapped 'phones and SIMs many times since then.