Hi Howard and welcome to GoY, depends where you live in the UK we can't in the north of Scotland but further south yes. If you can grow tomatoes outside then you can grow sweet peppers outside too.

I live in the south and my sweet peppers are covered with tall plastic corrugated sheets and already bear many small fruits. I tried them once in the open and wasn't very successful. They probably need some temporary cover, or be grown in a sunny location sheltered from the strong winds.

They are mediterranean plants and although they will grow they are slow and the fruit hardly ripens......thereagain if we have a hot summer who knows!
I grow mine in the gh and other than last year ripen them easily through until about october
I feed regularlywith a tomato food