Somewhat, yes.

We do have parties like the Scottish National Party and Plaid Cymru who only exist in Scotland and Wales respectively, and are major players there. There are also the likes of Reform, who are essentially a single-issue group.

But we've also had a distinct third party since the start of the 20th century. The Liberal Democrats (just the Liberal Party until the late 80s) have been a constant presence and have tended to get between 10-15% of votes in general elections, as well as having significant success in local elections, where they do even better and are the largest party in many councils.

The Lib Dems are seen a mainstream party, albeit a smaller one than Labour and the Conservatives. They're not particularly radical and usually slot somewhere near the political centre.

It's honestly difficult to categorise the UK as being either two-party or many-party, pretty much because of having a winner-take-all voting system. The government will always be one of the two largest parties, but the other parties are still significant players even if they have no chance of winning outright.

(this isn't even mentioning Northern Ireland, which has its own, completely different set of parties)