You have no worries whatsoever.
It would seem that a false representation has been made using an unauthorised copy of your signature.
To misrepresent a document in order to make a financial gain is regarded as an offence under the Theft Act.
I would seek you contact your local Trading Standards Office....do not bother with Consumer Direct....find the local officers.....if you tel of who both insurers are I will forward your experiences to the Insurance Fraud Bureau along with the FSA and the insurers concerned...
This site appears to object to contact emails being given in order to assist. It may be because of their association with so many insurers.
If either insurer has offered a solicitior who is acting after being appointed by the company for and on your behalf...tell them....they will ost certainly be in breach of oh so many Solicitor Regulation Authority regulations.....but then again.....it would seem so many insurer solicitors are unconcerned with the reality of the conduct of 'insurer appointed companies'
The reason your signature may well have been used was to place it upon documents used by the Association Of British Insurers General Terms of Agreement.....insurers/appointed hire companies use the documents under this agreemnet to ensure limited claims values and prompt payments for those willing to conduct themselves in the manner that led to the threats to you.
But there we have it...modern business practices that seem somewhat devoid of correctness or fairness....
R