Update

Well I have been having fun adjusting my HF whips for 40 metres and 20 metres. On 40 metres all seems to be ok, I have a reasonable bandwidth and pretty much in the middle of the band.

On 20 my antenna seems to want to resonate on 13.9Mhz, there is no moving it, shortening the whip section results in a very poor SWR. This means the antenna is just about useable uo to 14.2Mhz, its a very good match on the CW end of 20 but I am not sure CW mobile is a good idea!
I have heard mixed reviews of this type of antenna, some users have reported they cannot get a reasonable match at all so perhaps I am doing fairly well. In any case I have head Indonesia and a mobile VK station on 20 so far so the antenna is certainly receiving ok.

Both antennas are the kind with a rigid helically wound base and an adjustable steel whip. The total antenna is around  7 foot (2 metres) long with the adjustable whip section being around 4 feet (1.2 metres). I also need to change the site of the HF antenna to the right (offside) of the car, the spot where the VHF antenna is located. The reason for this is the HF whip keeps hitting overhanging tree branches. changing the antennas over will mean re routeing the cables in the car so that may have to wait for a while. I have now added a spring at the base of the mount to give a bit more flexibility.