Was the sun it got in the morning or afternoon?

Sounds like a drought problem - as you live in Hampshire, I'd guess that's the most likely explanation. Bear in mind that new plants have roots which are still pot shaped after you've planted - it takes a while for them to put out their own water seeking roots, so if you've watered by giving it half a can with the sprinkler on, its nowhere near enough -or if you've not watered it at all. Leave the hose running at its base on a very slow trickle for an hour (yes, I know its raining today, but do it anyway, and yes, in the rain, regardless). With any luck, the roots will actually get some water they can work with, rather than its being out of reach in the top two inches of soil.

Hi - I would say it got some sun in the middle of the day. And I've tried giving lots of water so will see what happens - thanks to both of you for your replies.