Your park is almost certainly on a business tariff, which does not have any "cap" like a domestic tariff, so when their contract for the 16p rate ended, they were at the mercy of whoever would give them a new contract.
You could ask to see a copy of their bill to check that the rate they have charged you is indeed the rate they have to pay (they cannot make a profit from the resale of electricity).
Looking at the current average business rates according to Moneysupermarket, it seems that your park may have managed to get quite a good replacement fix, as the average business rates are now in the region of 75-80p per kwh.
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