Irish Steve,
I would write to the operator (by recorded delivery) explaining exactly what has happened so far and inviting them to let you know how they plan to resolve the situation. You may also wish them to pass a copy of the letter directly to the pilot involved as well.
In the meantime, you can contact their local County Court and ask for a Small Courts Claim form. It is this, plus a fee, which you would then submit to bring about an action.
Bristol County Court
Greyfriars
Lewins Mead
Bristol
BS1 2NR
General Enquiry: +44 117 9106700
If Centreline do not reply, or decline to put it right, then you should advise them that you will take the matter to the Small Claims Court for judgement. As I understand it, if you win, you will not only get your goods back (or be compensated) but also can claim the fee as fixed costs.
Try a Google on UK Small Courts Claims for further information.
This seems comprehensive
http://www.netlawman.co.uk/info/small-claims-advice.php
Information and FAQs on the form (including some specimen letters you can send to rogues before going to court) can be found here:
http://www.hmcourts-service.gov.uk/c...ex301_0405.pdf
(None of the above is qualified legal advice, see various UK solicitors or UK Government websites for full and proper information.)