I'm remembering some stuff because we had a problem when our new boiler was put in.
At your meter, the pressure should be 20mbar or so, and not much less. If the pressure at the meter reads 20mbar but the pressure at your boiler is much lower, then its your problem to improve your home piping to 22mm etc.
We had the problem that the pressure at our boiler was <<20mbar when the new boiler was cranking hard. Immediately the Transco guy measured this (it was 2mbar if I remember correctly!), he turned off our gas supply and put in the emergency call. Transco came the next day (we were prioritised due to very young children at the time). They didn't need to increase any pipe diameter, but the old pipe (street to our meter) was clogged with 80 years of "gunge". They blew it out and inserted a new plastic pipe inside (thats quite a trick, seeing as it crossed the entire road underground and then did a 90 degree bend in our solum).
Because is was on the "grid" side of the meter, it didn't cost us a penny. Don't ask me about Transco's costs though. In fairness, this would have been a problem with any boiler, but the most likely time to spot it is when your new combi goes in. Telltale signs are the cooking gas hob burners going out when the boiler kicks in. Our combi boiler seemed to be quite happy on 2mbar by the way, although the gas engineer was astonished it was working!
I suspect that the gas main pressure does NOT need to be increased above 20mbar since the "peaky" combi usage per household will tend to aggregate out over the neighbourhood. Also, there is a tremendous volume of gas in the mains and it provides a nice storage reserve in itself. I believe pressure is deliberately increased a tad by Transco when high demand is forecast for this reason, and its called "linepack" if I am not mistaken?
Dr. Andrew Roscoehttp://personal.strath.ac.uk/andrew.j.roscoe