Increasing water pressure by widening pipe from main outside

First thing to do is to get a flow reading from the tap using a bucket. For example, if you can fill a 4.5 litre bucket in 30 seconds with the tap turned on fully, the flow rate from that tap is 9 litres per minute as per there supply, if you are not getting enough flow rate then the main thing to do is call out your water authority to check their Outside stop valve. This way you will know when they come out that they are supplying you with the correct flow rate. What you don't want is to fork out the cost on a new main your side to find it may not have been necessary. Then take it from there.

if you install megaflow you would probably have to increase main anyway ,thames water dont get involved within your property ,good builder will dig 750mm deep trench from toby in pavement to your main inlet ,increase change to plastic main ,cover in shingle and backfill ,plumber connects internally ,thames water changover at mains toby ,notify thames in advance to starting and get their date before you start your end