Kitchen tap twisting?

Our tap has a movable arm but the whole unit has now become loose and the whole tap unit is twisting when moving the arm.
I've looked under the sink and I see a spindle thread and nut directly under the tap. I've tried tightening it with fingers but its seems tight. There is no way to fit a spanner, it is directly in the very corner of the unit underneath and has the 2 water pipes in front of it with the gap being I'd say 2cms. I've heard of a flexible spanner but I'm not even sure it would fit in the gap plus the spindle hangs about 4 inches down and the nut is at the top.
Any ideas and help welcome thank you!

Advice from 1 local tradesperson

they sell tap spanners for that very job they are like long hollow tubes so you can reach up ill send find a link copy and paste it
https://www.toolstation.com/mono-tap-back-nut-box-spanner/p16973?store=B3&utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&gclid=EAIaIQobChMIjviNrYX66AIVGtZ3Ch0maAYYEAQYBCABEgKJz_D_BwE

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