I don't think there are many big UK computer companies that haven't been absorbed by something else.

There was Microfocus: https://www.microfocus.com/en-us/home They owned SuSE at one time. But MicroFocus now have owners outside the UK.

And there was Autonomy: https://en.wikipedia.org/wiki/HP_Autonomy Bought by HP, leading to lots of controversy and legal wrangling when they did get what they had expected.