Interestingly I got an email from FXCM regarding my spreadbetting account. I can't find any more info on their website about this as they still offer new accounts for spread betting or CFD but there is no mention of the difference between a "Spread Bet Pricing Model" and an "all-in" commission free pricing model.
FXCM Pricing Notice: Discontinuation of Spread Bet Pricing Model
Your account(s) is currently under the Spread Bet pricing model. Your account will be updated to our “all-in” spread offering at ............, after market close, while keeping all your spread betting tax benefits the same. Under the “all-in” spread model your trading cost will continue to be the spread, which you can see directly on the trading platform.
FXCM Pricing Notice: Discontinuation of Spread Bet Pricing Model
Your account(s) is currently under the Spread Bet pricing model. Your account will be updated to our “all-in” spread offering at ............, after market close, while keeping all your spread betting tax benefits the same. Under the “all-in” spread model your trading cost will continue to be the spread, which you can see directly on the trading platform.