I went rockpooling at home in Devon with my Dad and we found this fish under a rock. It had a sucker on it's belly which looked like it was made with it's fins stuck together. It was a brown/green colour and it had two blue spots on it's head and other blue markings. Thank's. Tom.
This is Lepadogaster lepadogaster - the Shore Cling Fish. It only grows to about 8cm long and does indeed have a "sucker" formed from the pelvic fins.
Preferring slightly warmer waters they are most often found in the the southwest of England, south to the Mediterranean.
I wonder where you were on the Devon coast. Maybe Meadfoot Beach at Torquay, or Wembury near Plymouth. Both are brilliant rockpooling sites that will offer these little fish and other wonderful shore creatures.
For your interest, "around lunchtime" on the 10th March 2012 should be a good time to go rockpooling on the south Devon coast as it is a good "spring" tide - when the sun, the moon and the earth are positioned to produce one of the lowest tides of the year. Always know the times of the tides where you go rockpooling to get the most out of a visit. The tide always seems to go out slowly, but seems to come in very fast when you are hunting in rockpools. A good site, which will give local tide times around the UK is www.tidetimes.org.uk. - Tide times differ from place to place so local times are essential - know the tide times and be safe.