Can't help with the two you have mentioned Steve, except to say that BAR seem to like the Nikko, but a bloke on a forum who recently bought one, got rid double quick. The Panamax range are all 50mm I think. Personally, having recently bought a Vantage with a 50mm objective I have made a decision to stay away from 50mm in future. They're big, heavy and can affect the balance of a gun adversely, and the sight picture is no better than a decent 40mm lense.
As for the Panorama it may be a safer bet. I haven't looked through one but the glass is supposed to be superior to that on the Vantage (old HD Sport), which is just as well, as the Vantage is no more than you would expect of a budget scope.
As for other options, if it has to be 4-12, the Bushnell Trophy XLT AO is available at £175. It focuses down to 10 yards and is said to be springer proof. Don't know what the new ones are like but the older models were well regarded.
For about £230 you could get the Vortex Diamondback which is also good for airguns. This scope is very well regarded indeed. If I could afford one, I'd order it today, but funds have been limited recently.
But when you add up how much you have lost on buying items only to sell them on, there is a lot to be said for paying more in the first place for something you will want to keep.
There's always the second hand route. You can often get a bargain. I know there are wide boys out there, but there are also people offering genuinely good deals. Over the years I have lost track of the mint equipment I have sold at two thirds of its original price. And I do mean mint as most of it had had very little use, and I take care of my things anyway.
If you could make do with 3-9x40 ao, then I can recommend the Nikkon Prostaff EFR for clarity. It's a very nice scope for £175, specially designed for rimfire and airguns (springer proof) and focuses down to 10yards. I have one myself.