You can simply buy a set of long reach monobloc sockets.
Rothenberger is one brand.
Any good plumber has them.
Only a few pounds. Basically box spanners
Isolate water supplies. Disconnect the tap flexis, move them aside and I'm pretty sure you'll get onto that tap nut with a standard monoblock box spanner.
Or just cut and reroute the condense pipe.
20 minute job either way.
What construction is your worktop? Is it laminated chipboard? Look closely around the base of the tap (on top) is it deformed into a depressed bowl? Could be that water has got in and turned it to mush which is why it needs retightening so often... Or just not tight enough in the first place!
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