I recently discovered Jessica Hann’s website – she does the voice of Mike the Knight’s sister Evie (who is, incidentally my favourite Mike the Knight character). And from her website I found out who did the dragons’ voices – each of which had been bugging me for a while as being semi-familiar.
Sparky is played by Colin McFarlane, who brings a certain presence to whatever he’s in. You may recognise him if you’re a fan of Torchwood, or Judge John Deed, or Reggie Perrin.
And Squirt is Russell Tovey, probably best known for Being Human, Him & Her and Gavin & Stacey.
Incidentally, Colin McFarlane also plays Harrison in Chuggington.