First thing that needs to be said is a 2:1 is a 2:1. It's as easy or hard to achieve at any university in theory, the difference is the quality of teaching, student support and how hard you get pushed differs at various universities. Perfect example was at my university in Lampeter this year we had UCL Cival Engineer Students surveying the campus from 7am to 10pm every week day for 3 weeks as part of their course, they are being pushed hard to get their double firsts I imagine whilst the lecturers at my institution are simply pushing everyone to get a 2:1 tops because they think thats a great result for them and us. This is why I wanted to leave the university, my personal tutor who is also head of Archaeology takes great pride that in their uni they have as few fails as they do in most top 20 universities. But I don't see that as something to be proud of if you create a glass ceiling, which in effect is what Trinity St David do.
What you need to do is message the admissions tutor of the university/universites that you are interested in moving to, explain your situation and see if they are willing to accept you. I did this in February a I didn't like Trinity St David, and I've got a switch to Cardiff. In general, there are 4 critera they will look at, 1. Your current performance. 2. Module similarities between institutions. 3. A Levels and 4. Whether they have any space left on the course. Obviously spaces free up with people dropping out of university but they fill up with other people wanting to swap, and theres an added problem that with so many looking to go to uni this year, they may cut the year 2 transfer intake so they don't get fined.
But theres no harm in trying, but you'll want to get at this pretty pronto! Good luck