Water pressure?

Do you have well water, or are you connected to a public water system?

I am connected to a public water system.

OK. Your explanation's a bit weird, so I'll assume you mean that the pressure starts high and then gets lower. If that's the case, it could be a problem with a pressure regulator in your house. Click this link and see if the thing looks familiar. They're usually located in the basement, either near the main water pipe, or up near the ceiling:

Do you have this problem at ALL the faucets in the house?

Do you have a pressure regulator?

Are the pipes copper (hardly ever clogs) or galvanized (often clogs)?

From the description, it sounds like there is pressure when you start, but if there is a clog, the pressure would drop on the far side of it.

Sounds most like thermo pressure build up from the water heater. I'll bet if you install an expansion tank, the problem will go away.

Thanks for this. The answer to your question is yes, it does apply to all the other faucets. I should've explained myself with more detail, when I turn on any faucet, either in the bathroom or kitchen the water surges out quickly and then drops to normal pressure and then continues to surge sporadically. This also happens when I flush the toilet. I wonder whether it's due to the cold weather and that my hot water has been temporarily turned off for the past 10 days due to my back boiler being too old and therfore disconnected by a Corgi registered plumber?

Thanks for this info. I'm not sure whether I have a pressure regulator or the type of pipes, this I will check.

I can't answer that last question.

Did you find a regulator in your basement?

Thanks for the info. If I do need to install an expansion tank what sort of figure should I be looking at?

Hang on a second - does this happen with hot OR cold water, when run individually?

As I live on a second floor flat, would you think this is at the communial area on the ground floor or with my own water tank?

Only the cold water as the hot is temporarily turned off and will not be turned back on until I get a new back boiler.

Are you home right now? Do you have access to the basement?

In that case, I think Steve Barker's suggestion is for a different situation. Back to square one: Find the regulator.

Do you own this place, or do you rent?