Well, after a summer without the problem showing it's head, the mornings have now dropped in temperature and the problem had returned.
I bought a replacement relay for the fuel pump (located above the fuse board behind the glove box) and fitted that on Sunday. Monday morning was the coldest of the year so you can imagine my delight when it started first time, no hesitation. Such a relief to have sorted the problem with a £6 relay and 30 minutes of my time.
Thanks again for all of the helpful comments