1 bar pressure is about 10 metres head, i.e. it is what you would get from a water tank 10 metres above you, and it is what you need to fill a tank 10 metres above. This is about enough even for a 3-storey house with a loft tank.
You would improve the flow (but not the pressure) by running a new, larger water pipe out to the pavement, assuming that yours is an older house with a typical half inch or 15mm supply pipe, which is very restricting. If you are one of a group of houses fed by a single small pipe you are doomed unless it is replaced by a bigger one.
You are not allowed to pump from the main (except for limited amounts) because if you are sucking from the pipe, you may prevent your neighbours getting any water at all, and you may cause dirt to be sucked into the main.
For an unvented cylinder (not tank) such as a Megaflo, you need a good incoming water flow. 20 litres per minute would do. A new water pipe is often necessary to get the best out of them.
If you have lead pipes, ask the water co to test your drinking water for lead content. There may be a subsidy to replace them, and the water co may replace its own lead pipes, if any.