CAJ,
Please can you tell me the following without giving any specifics, obviously:
1) Where was the job advertised? Was it through a "reputable" source e.g. your local job centre or in a national newspaper rather than the local rag?
2) Looking very carefully at the job description for your new role, does it clearly set out what you will be required to do? If the job requires you to do any selling, look very carefully at their clawback policy.
3) Have you got a copy of the new company's Employees' Handbook?
4) Look up the company here:
http://www.companieshouse.gov.uk/. Are they who you think they are? Look specifically at the "Last accounts made up to" section - have they filed their annual accounts within the last year? If not, you MUST treat them with extreme suspicion.
5) Have they explained to you just how much a company car will cost you in tax? If not, why not?