It is NOT a gecko... it is a newt... and by the looks of it a smooth newt Lissotriton vulgaris
Let me give you a quick lesson in identifying newts and lizards of the UK.
Firstly there are no wild 'geckos' in the UK. We have 2 native species of legged lizard (common and sand lizards), both of which have scaly skin and would be much too fast for you to hold like that, and would probably have drowned in a bucket they could not climb out of. They are very uncommonly found in water and are more likely to be seen basking on rocks. We do have a 3rd lizard species but this is the slow worm and has no legs and looks much more like a snake than a lizard.
Newts have skin similar to frogs, i.e. without scales. They are semi-aquatic species commonly found in ponds and (when out of water) in grassland and garden habitats. They are good climbers and can climb vertical glass surfaces when damp. There are 3 native newt species, two of which look similar to this one (the smooth and palmate newts), and another which is 2 or 3 times the size and is jet black with white 'warts' (the warty or great crested newt). These animals are sluggish walkers and a relatively quick swimmers. They do not like to bask in the sun.
May I suggest you let this guy loose in a cool damp area of your garden late at night when the sun is low or down, or at the very least move the bucket into the shade and let him climb out on his own. If the water heats too much in the sun the newt is at risk of death if it cannot climb out fast enough.
He has probably been munching happily on your daphnia.
Hope you found this useful and can now be somewhat confident in identifying native newts in future.
