If you are exporting goods to Ireland or Northern Ireland, you do not need to file an export and import declaration. Ireland is part of the EU and is therefore treated the same as, for instance, Germany or France. Northern Ireland, although officially not part of the EU, is de facto treated as such.
A lot of traffic to Ireland and Northern Ireland passes through Britain. To transport goods through Britain without having to file an import declaration there, you need to prepare a so-called T2 transit document. This document grants you permission from UK customs to travel through their customs territory without making an import declaration and paying import duties. However, you do have to post a bond equivalent to any import duties plus VAT and excise duties that would be due on the goods if they were indeed to be imported into Britain. When the goods under transit leave Britain again and reach Ireland or Northern Ireland, customs will then release the bond.
Boom Customs is authorised to prepare these necessary transit documents and can post the bond on behalf of the carrier or the owner of the goods.