Aer Lingus is working closely with BA (they used to be part of Oneworld and still have codeshares) so I am pretty sure they should be able to check your luggage through. They do mention it on their website as well:
Aer Lingus will through-check baggage as a courtesy onto any carrier that have a baggage agreement in place, upon presentation of documentation of the itinerary showing Aer Lingus and partner carrier flights on the same ticket.
This includes the following airlines: American Airlines, Air France, Air India, Alaska Airlines, Finnair, British Airways, Air China, China Airlines, Cathay Pacific, China Southern, Emirates, Etihad, Gulf Air, Iberia, Japan Airlines, KLM, Kenya Airways, Kuwait Airways, Malev, Malaysian, Martin Air, Northwest, Austrian Airlines, Pakistan Airlines, Qantas, Qatar Airways, South African Airways, Singapore Airlines, Thai Airlines, United Airlines, Sri Lankan Airlines, US Airways, Virgin Atlantic and JetBlue Airways.
I have not been able to find a similar list for BA but I assume that it works in the other direction too.
Belgium, Ireland and the UK are all in the EU so customs and security should not be an issue.
The most important thing is to book both flights on the same ticket (e.g. from a travel agent or one of the airlines). If the connection shows up on the airlines' websites or on a travel agent's system, it means that it does meet the guidelines for minimal transfer time and that they should take care of you in case of problem.
If you book each leg separately, you are on your own and they might even refuse to check your luggage through as matter of policy.