Yes, that is true - if you can reasonably expect that you will not be on one particular assignment away from home for less than 2 years you can claim your car expenses at a rate of 40p a mile up to 10,000 miles per annum. Most employers would reimburse you themselves, and in this case you could not of course claim any further tax relief.
You can also claim subsistence and accommodation costs up to set limits if your employer is not providing you with these.
Having just re-read that I realise the first sentence shoud read "if you can reasonably expect that you will not be on one particular assignment away from home for MORE than 2 years" .
Basically, any move to a different workplace that is expected to last more than 2 years is regarded as a permanent move and travel expenses have to be borne personally.