That helps a fair bit
However considering it would involve 4 flights on the way out and a lost day on holiday it's a little ridiculous. On the other hand could just go with hand luggage to Ireland the night before then land in heathrow, go home and pick up holiday stuff and come back*...
It still doesn't explain what is going on for UK flights on the 1st April. APD is going up by a couple of £, certainly not the £300 the flights are going up on the 1st April. Is this happening elsewhere as well?
*Not sure that would actually work but shows how silly all this stuff is!
EDIT:
For comparison, exactly the same flight from London...
For 200 quid I wouldnt do it... Because you will pay for flights into Ireland + baggage costs...
I mean if you have a party of 4+ people then there are some savings to be made, but if you are on your own... doesnt sound so appealing you would be saving around 120 quid at best.