Polypetarus? Those fish are common to find in UK, was once rare to people started stocking up hard. It's a bit like the celestial pearl danio aka microrasboras galaxy...
Oh and also, someone mentioned a cricket being like a car alarm?
Was it really a large cricket?! In which case, it would have been a Weta, but I don't think they are in that area, so it was possibly a cicada?