This is a Commodore Pet
My very first computer was a Commodore PET 2001. 'PET' stood for 'Personal Electronic Computer. It used a MOS Technologies 6502 CPU, 4KB of 8-bit RAM and a 9-inch (green) monochrome monitor . It also had a built-in cassette drive (for storing programs) and a small keyboard. This was called a "chiclet keyboard" as its keys looked like the chewing gum of the same name. These computers were on sale in the USA in 1977 so the year was probably 1978 in the UK. I bought mine second-hand from a fellow ham.