Got back from a weeks holiday at Easter.
Immediately noticed hot water pressure in kitchen tap had dropped significantly so tried other taps & it turned out all hot water taps are affected.
Since then it's got worse. For a 6pm bath we have to start running it at 5pm and we've noticed that if the dishwasher, washing machine etc are running (even just one of these items at a time) the water practically stops - it literally does turn into a trickle.
The showers are not worth turning on now (let alone try & use)
If all hot water taps are running at the same time (which we did as an experiment) no water comes out of the showers at all.
We didn't think the issue could get worse but we have an 8 month old DD and a dog & it's now getting on our nerves.
The water board don't want to know. The plumber we have managed to get out shrugged his shoulder & said he'd be back.....but never was 

The water bar pressure has dropped on the boiler a little.
Any ideas?