There used to be a dedicated Social Security tax of 1/6 in the £ (7.5%) that funded superannuation. I forget when (perhaps the Muldoon govt?), but it was subsumed into general revenue with the understanding that taxation would continue to fund super.
That said, I think it's sensible and fair to raise the entitlement age, and probably sooner than Labour is suggesting. I'll be getting it in 3 years, and I wouldn't mind if I had to wait a couple more months. But because I have contributed all my life, as above, something I tend to see as a bit like a contract, I'd oppose means testing.