Make sure you travel light so you don't get charged when you bring one back! Think you can save up to 15-20% by buying it from UK. Downside may be expensive support from Mighty Velo if you do need help (unless you're technically proficient). There are a fair number of options involved in buying one so decide early before you go down - color, gearing options, handlebar type, rack/fenders/none, luggage options, lighting, etc.
Most overseas suppliers tend to only carry single-color bikes (red/red, white/white, etc) in the shop and require you to wait months if you want a specific dual-color option (red/white, black/yellow, etc).
That seems a weird alternative. Buying a Moulton and buying a Brompton are two very different considerations lol.
I'm not that familiar with Moultons though I know the ride quality is supposed to be great. Brompton's probably can't beat it, but then a Moulton can't touch the compactness/transportability of a Brompton fold.