Water Boards have to supply a minimum 9 l/min at your boundary, i'd be checking your neighbours flow rate, if thats greater than yours then you know the problem lies after where it splits off to feed your property.
Who is your water supplier, as Jamie mentions, 9l/min as a minimum is the norm. Is it a 15mm stop cock too?
@ 3.8bar pressure you should be getting a pretty good supply, you definitely have a restriction somewhere by the sounds of it.
Readings taken on the outside tap using a bsp pressure gauge and a slightly less technical filling a bucket and timing with a stopwatch.
Supplier is severn trent. Neighbours are fine so I assume it's the underground stop cock causing restrictions given that it's the only thing not replaced, bar perhaps the pipework between the outside cock and the kitchen tap.
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