This is sadly a prime example of following advice to update/increase the incoming supply pipe diameter typically dispensed on this forum.
There is no way a respondent on this forum would know how much improvement a larger pipe would make, without measuring the flow rate at the road demarcation point first. And this hasn't been done or proposed.
Unfortunately you have wasted your money - I can think of at least 4 customers I have been out to who have read posts on this very forum and been convinced of the merits of upgrading their supply pipe, only to get what one could describe as a marginal improvement, and had to look further afield.
For anyone in doubt, the fact that your static pressure is 3bar does not mean that you will get more flow rate when the incoming pipe is enlarged. You must first ask your local water supplier to measure the flow rate in the street at your isolation point and put it in writing, this will be in litres/minute.
Only then, with this information to hand, will you have the data upon which to justify £1.4K. Alternatively, you will have tacit proof that it isn't worth doing if the flow rate is only 3l/m higher at the pavement connection.
NB: If you have 3bar static I can guarantee an accumulator will resolve the problem, without measuring the incoming flow. This is because with an accumulator you are buffering a large volume of water in your own property at 3bar, rather like having a large charged battery on site. Unfortunately, that will cost about the same again.