Welcome circushead!
Unfortunately I know nothing of
Royal Mint return policies.
If the coins are still attractive, perhaps you shouldn't worry, but try to keep them from toning further. If they've been in a damp area, put them where they'll stay dry- perhaps toss some silca gel packets nearby to absorb moisture. Try to keep them where they won't be exposed to temperature extremes, particularly heat. You may want to put them in airtites, or intercept shields- the latter have absorbants/chemicals designed to neutraize trace harmful gases such as air pollutants. Latter run about US $1 each, former a bit less. If you do transfer them, handle them by the edges, and consider wearing cotton gloves so as not to scratch or fingerprint them. Here in the US, some feel that white plastic trays some mint products come in which support the actual clear plastic coin holder may cause toning or hazing. nohope587 is a board member here who is knowledgable re coins and is a British expat. I think he is currently off on business, but he may have some useful advice/input when he returns-he is also the numistmatist who tipped me off re the US mint plastic trays.
Don