Lancaster doesn't require FM and is 9th for Maths in the Uni league tables.
That's too simplistic.
Oxford doesn't require FM... however if you look at the statistics they accept a considerably lower percentage of candidates without. It's 0-3 a year with as many years being 0 as 3.
What would also be interesting to see would be what proportion of those who don't take further maths get accepted overall and of those who do, how many drop out.
Because when I did maths, it was assumed that you had done the FM syllabus. You would struggle in the first term because you'd be playing catch up. Maths is a big enough shock at degree level (it's nothing like A-level or FM in areas!) without finding knowledge that you don't have is assumed. I struggled in statistics because I'd done none.
And from Lancaster's website they say:
A Level applicants should be studying at least three A Levels, including A Level Mathematics. We encourage (but do not require) you to study A Level Further Mathematics - this will make you eligible for a standard offer usually one grade lower than those who do not study A Level Further Mathematics. Please see the 'Our standard offer' tab below.
If it is not possible for you to study A Level Further Mathematics, think about studying AS Level Further Mathematics - the style of mathematics in Further Mathematics, especially Further Pure Mathematics, is similar to university mathematics and will be excellent preparation for your university studies.
Specifically note it says "if it is not possible", which implies to me that what they are saying is that they will consider candidates who were at a school that did not offer it, not candidates who did not choose it.