There's a one yellow with pink gills thats about 5cm long, a lot of babies that are white with pink gills around 2 cm long and a few browner ones with gills about 2cm as well.
2013 photos & vids here
eff37 on Flickr
Cin J
Possibly could be Smooth Newt tadpole, pic right at bottom of this Wiki article ... en.m.wikipedia.org/.../Smooth_newt
Just like you Caroline I have been googling & learning all about the lifestyles of various Newts & other related critters ... good way to pass the time whilst it's too hot for housework or gardening!! Lol
Another new term from livescience.com ... Baby newts, called larva, can feed themselves small shrimp and insect larvae they find while swimming around. Newt babies, called tadpoles, resemble baby fish with feathered external gills. Much like frogs, newts evolve into their adult form. Some go from egg to larva to adult, while others evolve from egg to larva to juvenile to adult.
They have different species & possibly terminology in US, sometimes get caught out if I forget to specify UK in my search!