Kelly amps were designed and built by John Kelly, his son also called John Kelly (and still fixing amps in London) and other ex-Selmer employees.
The Kelly amps are not surprisingly very similar to Selmer amps, but in my opinion are slighly better built. They sound really good although don't overdrive to the same extent as a Marshall. They can be picked up quite cheaply so, in my opinion, a really good buy.
Like many Selmer amps they have not ajustable fixed bias which runs the output valves very hot, so it is worth having any of these amps checked over by a competent tech. It is a very easy to convert these amps to adjustable fixed bias.