It would be interesting if they could get DNA evidence to confirm the relationship...but they should be more closely related to the Samaritans than to Jews, since Manasseh was one of the ten tribes of the northern kingdom, whereas Jews are mainly descended from the people of the kingdom of Judah. At least that's how I've always understood it...I could be wrong.
DNA is not precise enough to differentiate between Hebrew tribes that far back, or even between any other closely related groups then.
There's quite a lot of DNA evidence connecting today's Jews to each other and to other Middle Eastern people, and none connecting peoples of the British Isles to either.
The best the British-Israel folks can come up with is that the original Middle Easterners were all displaced to the northwest and all those people there now (as well as today's Jews) came from elsewhere.
I can post links if you're really interested.
The Samaritans are supposedly Medes/Persians and others with no Jewish ancestry of any kind who were sent to Israel by the Persians to supplement the population of those returned from the Babylonian exile.