Not quite that simple, blackadder.
At the risk of 'being a bit boring', the actual situation is :
The GPs will get a payment for every **confirmed** diagnosis of dementia - which will still need to be done by referral to the consultants. So they don't get the cash quite that easily.
It is definitely in their interest to do some initial screening though & refer appropriate people for a proper diagnostic test.
Which is a good thing - the earlier the diagnosis, the better the drugs work.
You could argue that they should already have been doing the screening (and my surgery certainly has - even had me in to do my talk) ... but ... we live in a money-driven world (for some people) and the incentives might just work.