Those are left wing positions. Until 2023 the UK's Green Party's policy was to leave NATO, and there is still a lot of support in the part for that. When the UK's Labour party was socialist they were anti-EU. If you look at campaigned for what in the 1975 referendum on EEC membership its pretty clear: for example, Thatcher campaigned to remain, Tony Benn campaigned to leave. The remnants of the old left remain anti-EU even now.

They're neither wing. A foo-wing person could want to leave the EU because it's too bar-wing for any values of foo and bar.