How much of a contributing factor? Is it a big number?

I would expect most immigrants to be of an age where they present the least burden to the NHS.

The ageing population - i.e. that which places most burden on the NHS will be predominantly British non immigrant.

IMO the biggest contributory factor on stretched public services are domestic policies of "austerity".

How many of those immigrants work in public services?

As Bren2k posted earlier, the Tories and their press have been very, very, successful at planting the seed of "immigrants being to blame" for the NHS being overstretched.
Baring in mind that the most expensive patients are the over 65 (£6,000 p/a) and the over 80's at (£8,000 p/a) but, "everybody" believes "them" all to be health tourists.
How, when ALL public services have been slashed, can the Tories still manage to sell a lie, it's quite incredible, anyone would think that they had friends in the media and an impotent opposition .

Furthermore - the single biggest cost to the benefit bill is pensions; certainly not immigrants, or even fraudsters, or scroungers with 16 kids and two council houses knocked together. Despite that, the narrative around benefits is always disproportionately skewed, to the point where a whole new genre of 'benefit porn' reportage has been spawned, dutifully trotted out by the Daily Fail and it's lower rent counterparts - and somewhat incongruously, Channel 4.

The Tories have a long history of dividing the working classes in order to conquer them - and they've done it with stunning success to embed the idea of 'austerity' as a requirement; whilst quietly overseeing a £555 billion increase in government debt since 2010.

Potentially brexit could be a disaster, certainly it can't be resolved in a two year time slot. The one piece of good news I read today was an idea that until trade agreements are reached ,we would work on a zero tariff trade basis. This may take up to ten years but probably gets everybody off the hook. Also a lot can very obviously happen over ten years.
I would think whatever the outcome we will have to make some financial contributions. It's highly unlikely we will get any decent deals without some kind of payment.

Thing is it's all so unnecessary. With all the problems in public services, housing etc Brexit is likely to be as welcome and as distracting as a fart in a space suit.

Harsh but true.

Nothing to do with our enormous national debt then?

Which as I've already pointed out, is even more enormous after 7 years of Tory rule than it was to begin with; so they've increased the national debt by £555bn, but continued to massively defund the NHS - because it's a deliberate, ideological strategy to privatise, and nothing at all to do with 'reducing the deficit.' And immigration is a red herring of epic proportions - the biggest impact immigrants have on health and social care, is to staff it.

Thanks bren2k, summed up perfectly.

You should also consider that Britain produces more EU migrants than any other country within it.

Which means any reduction in immigration would be tempered by a reduction in emigration.