Thank you for all your ideas! I tried a very cheap mount that slotted into the air vent and it did a reasonable job. It wobbled about a bit and I though it might fall out but it didn't. And the free sat nav app, navfree, was very good and made sure I didn't get lost.

I think I will try one of the many matts that sit on the dash top and hopefully that will be more secure than the air vent bracket. I also have another cheap bracket with a big sucker for the windscreen but it looks very ugly even if it will do the job well. I shall keep it in the car as a last resort!

Go to a double glazing company and buy a roll of rubber bedding tape that is used to bed DG units onto wooden window frames. It's really sticky and use it to stick the disc to a flattish part of the dash. My current ones have been in place for nearly 4 years now. When you want to take it off to sell the car it doesn't leave a mark or sticky residue.

I think you'll only be able to claim that once you try and remove it. Its remarkable what sunlight and much heat can do to adhesives over 4 years.

Already done it several times brum - pulls off when cool and a bit of a scrub with meths followed by armorall does the trick.

Better than the horrible sticky mess that the manufacturers pads leave when they've been in the sun for a year or two.