Slovak koruna is one of the strongest currencies in world during last time
Because starting from July the ratio to Euro will be fixed I think that the only difference is during next mont. Moreover it is unclear which one exchange rate will be negotiated with EU/ it does mean that it must the actual one, it can be average for some period/.
So your question should be: what will make GBP/EUR during half year?
I personally will convert pounds immediately in Slovak koruna.