You can't feed ovens, immersion heaters, etc from a final ring, but that is to stop overload need the consumer unit. You are looking to do reverse, and what you would need to do is look carefully at the loading. And what MCB's or fuses or RCBO's are fitted.
So with a 10mm feed cable from a 45A MCB for example you would need to fit a mini consumer unit in the island so each item could not use excessive power.
With a 2.5mm feed from a 16A MCB then it will already be at it's limit.
Between the two you have to work out loading and safely limits. It may be possible, but there is no 100% answer until one knows exactly what the circuit is.
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