it is possible to book vehicles in UK without CDW depending on preferemces set in profile ( assuming a gold member ) or by country booked from.. I find it tends to be a lot more expensive though

When logged in and with CDW set to yes for UK in profile , I get a weekly rate from Heathrow of 538.76 GBP
When logged out and set country to US , I get a rate of 1206.19 GBP

If your card company declines to pay the GBP150 , I would suggest that you are likely better off than having booked without CDW

If you have a gold membersip, what does it say in your profile for Europe, Middle East and Africa vehicle preference for Collision Damage Waiver?

If the damage was there at the end of the rental, how is it a scam to charge for it?

You might as well try making the claim - given that it was included in the rate, rather than accepte as an extra on top, I suspect that you will be covered.