Even if not much longer useful info but still:
....In the European Parliament MEPs are not organised by nationality, but by political affiliation. They sit in political groups. Each group must have a minimum of 25 MEPs and have representatives from at least one-quarter (7) of the member states.europarl.europa.eu/unitedkingdom/en/european-elections/uk_meps.html
British MP's have (had) the same vote and voice as any other MPs....and since they are working in multi-national Euro-Parties they make policy for likeminded people across Europe.
Here are some of these political groups:
europarl.europa.eu/about-parliament/en/organisation-and-rules/organisation/political-groups
I guess british Labour MP's preferred to work with a different group than british Tory MP's....it's the same in every EU member state. A conservative EU group gains it's members from rather conservative european MPs...whereas the leftists and the Greens get their members from rather leftist and green political parties across Europe, for example.
So...the bigger the affiliation bloc...say, conservative or social democrat or whatever, the more influential it's ideas and wishes are...the bigger the chances it get's it's will through.
Sometimes these groups work together and support each other, sometimes they fight each other...some are allies, some are enemies...as in every democratic parliament.
Nobody cares about the nationalities of the members of these groups...it's the political affiliation that counts!
So, you should rather ask which political affiliation those 69 british MPs had joined, and how powerful their bloc was...
Even more soon-to-be-useles info for Brits:
2019 there had been european wide elections for the EU parliament...here you can see which blocs and affiliations are powerful and which are not so much...which group won and which group lost...
en.wikipedia.org/wiki/2019_European_Parliament_election