En suite in loft extension

[barnet boy]

My brother has recently bought a house where the loft space has been converted into a master bedroom with an en suite bathroom.
The boiler is in the kitchen on the ground floor and the water cylinder in the airing cupboard is on the first floor, just below the en suite. The cold water tank is still in the loft space, but on a raised platform.
The shower in the en suite is supplied via a shower pump and so no problem, but the water pressure to the sink is very poor.
I would like to 'T' off a new supply to the sink from the pipework after the shower pump, in order to increase the water pressure to the sink.
Is there any practical reason why I shouldn't do this?

[buildersmate]

No reason at all. These pumps are normally double-impeller, so they pump both hot and cold to equal pressure. You would need to take a T off both pipes. The temperature at the showerhead may go wonky during the few seconds the sink taps are on.