remmebr just a DIYer , i'm sure the more Pro guys will make suggestions
you may need some tools - i have various tap box spanners that fit - but often wont go around the nut - because of the ceramic -
This i have used just recently on a small basin where the TAP had come loose a few weeks ago.
Order online at Screwfix.com. Ideal for reaching, tightening and loosening most 15 and 22mm pillar and bath tap back and union nuts. Features durable iron rod handle and adjustable pivoting head with hardened steel jaws to offer easy installation and removal of taps. FREE next day delivery...
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BUT it depends on the Tap and how its fixed to the basin
some of the other tools i have
Fits 50mm A/F and 46mm A/F brass and nylon nutsNB: Some modern waste backnuts are slightly larger than 50mm and will need filing to fit and nut must be hexagonal not octagonal
www.toolstation.com
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A photo from underneath would help
hopefully it has an isolation valve