Taking profit depends on what your objective is. I think something to take into consideration is what your downside is. In another words, what are you risking.

If for example you want to take 50 pounds out of the market, how much is it that you can potentially lose. I'm not making any forecasts here, or suggesting where Bitcoin will go, but let's say it drops back to around $5000. You would have lost 400 pounds. Is that really worth it to make 50 pounds?

Most professional traders call this risk to reward. In determining this, you have to assess how volatile the asset is that you're trading. In this case, bitcoin is quite volatile, so you have a lot of exposure. But that volatility can also work in your favor.

If you're into technical analysis, you might be better off just choosing a spot that you want to sell based on your analysis. This way it has nothing to do with your PnL. Actually, that is how it should be. It's generally not a good idea to be too focused on your PnL, but rather watch and see which direction it is heading. If it's heading up, why would you want to sell? If there are signs that its reversing, it makes sense to get out and try again at a later date.