Well you should be a priority, as Ofwat measure water companies on pressure targets. It's called DG2 standard. Check out
Water pressure
And be aware that Water Companies live and die by these standards.
Did they contact you about this work, if it was planned, and not an emergency? If not then that's another GSS payment (see the link).
So, they may owe you £25 or more under GSS (Guaranteed Standards of Service). You should put this in writing. Not much help at the moment though.
If they still don't sort this out then CCWater (The Consumer Council for Water) are the people to contact, but 95% of the time it doesn't come to this.
Sorry, but I'm unable to advice you regarding the short term service issues, without a lot more detail on the nature of the works.
Hope it's all sorted out soon.