The legal limit on tread depth, which is part of the MoT is 1.6 mm - most safety organisations (all AFAIK) agree that 3.0 mm would be a much safer minimum depth, specifically in wet conditions, and there are moves to get the limit increased to 3.0 mm across the EU but getting that agreement is time consuming.

As others have posted, bite the bullet and buy replacements.

Could be, it maintains the "useable" amount of tread if the limit is increased. But it also gives the tyre a longer life under current rules, so reduced tyre carcass waste.

Looking in my copy of the Bosch Automotive Handbook, there is a graph of wet stopping distance vs tread depth. The stopping distance increases gently as the tread depth falls, but at about 3.5mm it starts to fall exponentially with decreasing tread depth. The stopping distance at 1.6mm is more than double that at 3mm.

That's why the authorities want to increase the legal minimum to 3mm.

And I agree. There are already way too many cars which fail the mot with worn tyres. if the standard were 3mm then at least they'd be failing with 2mm instead of 1mm or less. So a safer situation than now.

My analysis of the OP: go get a pair of new tyres on that axle, tight wad! Oh, and have the new tyres on the back!!