In general, to someone in a similar circumstance I might suggest that the lowest-risk option is to immediately convert your excess currency into the currency you will be spending. Note that 'risk' here refers only to the variance in possible outcomes. By converting to EUR now (assuming you are moving to an EU country using the EUR), you eliminate the chance that the GBP will weaken. But you also eliminate the chance that the GBP will strengthen. Thus, you have reduced the variance in possible outcomes so that you have a 'known' amount of EUR.
To put money in a different currency than what you will be using is a form of investing, and it is one that can be considered high risk. Invest in a UK company while you plan on staying in the UK, and you take on the risk of stock ownership only. But invest in a German company while you plan on staying in the UK, you take on the risk of stock ownership + the risk of currency volatility. If you are prepared for this type of risk and understand it, you may want to take on this type of risk - but you really must understand what you're getting into before you do this. For most people, I think it's fair to say that fx investing is more accurately called gambling [See more comments on the risk of fx trading here: https://money.stackexchange.com/a/76482/44232].
However, this risk reduction only truly applies if you are certain that you will be moving to an EUR country. If you invest in EUR but then move to the US, you have not 'solved' your currency volatility problem, you have simply replaced your GBP risk with EUR risk. If you had your plane ticket in hand and nothing could stop you, then you know what your currency needs will be in 2 years. But if you have any doubt, then exchanging currency now may not be reducing your risk at all. What if you exchange for EUR today, and in a year you decide (for all the various reasons that circumstances in life may change) that you will stay in the UK after all. And during that time, what if the GBP strengthened again? You will have taken on risk unnecessarily.
So, if you lack full confidence in your move, you may want to avoid fully trading your GBP today. Perhaps you could put away some amount every month into EUR (if you plan on moving to an EUR country), and leave some/most in GBP. This would not fully eliminate your currency risk if you move, but it would also not fully expose yourself to risk if you end up not moving. Just remember that doing this is not a guarantee that the EUR will strengthen and the GBP will weaken.