I'm not claiming it was overvalued for the whole of that time. But it was only in Jan 2015 that it started to go above a rate of 1.3 (unless you go back to 2008).

But you must realise (well, should realise) that looking at a graph of the exchange rate between the Pound & the Euro does not actually tell you much about the 'real' value of the Pound. That is why the page I linked to commented on comparing Sterling to 'a range of currencies'.
If the Pound rate improves when looking at the Pound/Euro exchange rate, it can mean either that the Pound is doing well, or the Euro is doing badly (or a bit of both).