Washing machine installation in bathroom. Electrics or plumbing first

it would be worth getting an electrician in first to check that it is possible to install the power supply to the washing machine in compliance with the wiring regulations as this could prevent the washing machine being installed all together.

please take in account that as per regulations it's NOT allowed to install any electrical point such as a socket in the bathroom unless it's 3m away from the bath or shower edge ( apart from the shaver socket in a safe considered distance as well ). you will need to get a qualified electrician who's aware about the electrical regulations all the best

Get an electrician & check whether a washing machine can be installed in that zone before carrying out plumbing work.

If you are planning to plug the washing machine into a socket outlet in your bathroom then the socket needs to be sited at least 3 meters outside of zone 2 in accordance with part P. Of this is the case then the plumbing should be prepared first then you can run the cable to the socket in question providing the cable is chased in deep enough and in the prescribed zones. Hope this helps