Can anyone tell me whether the VAC at Regent house are still pulling the passport photo scam and whether the British Embassy are doing anything to combat this?. Recently heard they were telling applicants that photos must be on a white background and not as per...

https://www.gov.uk/photos-for-passports

As far as I am aware, the UKVAC have never pulled a passport photo scam.

There have been complaints on forums like this from people who have had their photos rejected; often because they've taken the photo themselves and tried to cut it down to size or printed them at home and the quality isn't high enough. Of course, people in that position often wont accept that they are at fault and so complain of being scammed!

Make sure the photo meets the requirements and they will be fine. One way of doing so is to have the photos taken at the VAC. How does the price for this, 250 baht for 6, compare with elsewhere?

This guidance is more detailed than your link.