This is a really interesting question.
Were you sent a purchase order at any time for this work? I have no legal training, but any terms and conditions attached to that order might be binding if you have been deemed to accept them in some way.
Otherwise, it does appear that you have up to six years to send and invoice and expect payment within 30 days of its date - see this thread
For more definitive advice, if you are an NUJ member, it might be worth contacting its freelance organiser. The NUJ is, I believe, able to offer free legal advice to its members.