Try AMS/BOD/DUB/NCE in that order but from LGW only. These are (or were) the cheapest CEUCLGW fares - AMS was 173 (before tax) in the last fare PDF (which is now sadly defunct and out of date, so I'd expect that to have gone up a bit plus the taxes have gone up due to Gordon's Thievery...but you may still get it all sub 300 quid). Given you need C or J to qualify, anything else is going to be very steep. Oh, also factor in an additional fee to book the ticket in the correct fare bucket which ba.com won't guarantee - i.e. either calling BA telesales or using AmEx (flat fee 10 quid for your Platinum Charge Card travel service) or some other TA.