I believe Glen is probably right, he/she is most definitely a nursery web spider from the family Pisauridae, getting it to species would require a microscope. They range in colours from yellow,browns and deep reds, but the rule always being a single line down the thorax. They're really common throughout the UK and can be found basking in the sunshine on hot days. Usually from the head downwards they are 15mm, so you may have come across a youngster reaching its final moult. If you come across any more creepy crawlies do let me know, I'd love to I.D them, especially butterflies and moths