DNA suggests that Beaker people did replace Neolithics in Britain

[Imperial Dave]

initial contact with new Beaker folk, disease outbreak followed by westward migration/segregation and follow up of occupation of vacated lands

According to the celebrated authority wiki, the population of Mexico fell from 25-30 million to 3 million in fifty years.

that is significant and more importantly shows a parallel occurrence which could account for this 

[Andreas Johansson]

According to the celebrated authority wiki, the population of Mexico fell from 25-30 million to 3 million in fifty years.

I believe I've seen estimates of more radical decline, but they weren't in the book I thought they were from.

But (central and southern) Mexico was a densely populated place with relatively good communications: good conditions for epidemics to spreak. Would Neolithic Britain have been as vulnerable?

[Imperial Dave]

In the non mountainous areas, I suspect there was a reasonable network of communication with neighbours and even in the uplands there would have been contact. If the Mexico example took 50 years, I am sure that kind of timeframe is also possible for Britain

[Erpingham]

initial contact with new Beaker folk, disease outbreak followed by westward migration/segregation and follow up of occupation of vacated lands

I'm not sure about the migration - we'd need more samples that showed pre-Beaker DNA more prevalent in the West to prove it.  Segregation/marginalisation of remnants with some violent removals and some integration would do it, if the disease was virulent enough.  What disease would be speculation but DNA has been extracted from teeth to prove the Black Death was Y. Pestis so that might be a route to test the hypothesis.

[Jim Webster]

In the non mountainous areas, I suspect there was a reasonable network of communication with neighbours and even in the uplands there would have been contact. If the Mexico example took 50 years, I am sure that kind of timeframe is also possible for Britain

A naive population is still naive, it might have taken longer, or with less people it might not have taken them as long to die out. In theory you might find isolated populations on islands in the far north and west could have hung on, but the problem here is that archaeology cannot give us anything like the detail

[Imperial Dave]

no, the best evidence is datable DNA