The last brew in a pressure barrel with a new Ballihoo lid and C02 injector has behaved much better, problem solved hopefully. So I've got two pressure barrels, 4 Oxebar Monolayer 8L Kegs & Tapping Heads and quite a lot of bottles, so I'll be using a mix from now on, dependent on what I'm brewing (Ales barrels, Lagers in the Kegs......etc.)
By the way, the Monolayer kegs seem to work well, but you really need a tapping head for each of them, which make them not as cheap an option as first seems. However, I contacted Kegland in Australia and asked if they could provide them direct, they directed me via email to their Chinese distributor who let me buy them at a much better price than as advertised on AliExpress - they also expedited despatch and delivery, I had them in a week.