Any plumbers on the about? Whats actually required for one of these?
I've been in my flat for 6 months now, feels a lot longer! Just had a full years invoice for Thames Water come in, and its jumped from £28/m to £41/m

Just made me realise how much I am paying & I am on the wrong tariff.
£41/m is tad steep considering I live on my own! So rang them up, was told I could significantly reduce my bill (almost half it!) with a meter fitted.
I've looked I don't think I have one, (can't see anything which would resemble it) I can see the water feed coming in under the sink, its like any other house with a water pipe in and a valve to close it.
They said if one could not be fitted I would be put on a special contract, but hoping one can be fitted.
But whats actually required to fit one? Did a bit of research most of them are just propeller based, and just put on the main feed pipe?
Assuming something like this is bolted in?

There is plenty of space for one to be put in, any other special requirements?
My flat is in a 1930's building if that makes any difference :-/