Thank you all for your advice on this - I'm pleased to say that all the ducks lined up yesterday and I managed to get through the test successfully!!
It wasn't a pleasant experience - three hours in a glass canopy'd Robin in 30+ degress, having to go to another airfield to pick up fuel first (don't ask!), differences in what the CFI expected and what I'd been taught, poor vis whilst navigating through an area I hadn't flown in before, zero wind so poor performance from the plane both in terms of power and short field performance... I think I'm still suffering from sunstroke but it's starting to sink in now!!
I don't suppose there is any way to expedite the license from the CAA? Having read a few other threads, it would appear that all you can do is phone in to check they're working on it, and maybe go and collect it rather than waiting for the post?