I worked on the original project that underpins most flooding maps – the flood estimation handbook – on the hydrology bit. Those were the days!
I would look at the EA maps, get the history of flooding etc. Basically get the facts out and see what it looks like all together.
It’s not just river flooding you need to worry about mind it’s also the sewers. Your house may not flood, but the sewers often will back up if flooding happens near by and flood your house that way.
Personally, unless it’s very cheap or the area really hasn’t seen much historic flooding (i.e. look back over the last 100 years) I don’t think it’s worth it.
There is a flood database on the british hydrological society website where you can look for historic floods by river etc.