If you like them, buy them.
If you're on the fence and are mainly thinking of getting them because they're fashionable right now then £100 seems like a lot, because in 6 months they'll be old news and the new fashionable trainers will look completely different.
If you like them and they're comfy at least you'll still wear them, if you're primarily buying them to look current then they won't look current for long.