Bike polo mechanics & fixing

Square taper iso.

The freewheel is a BLB one.
It's not a cassette hub, there's no movement possible of the freewheel.
The hub is 135mm, the spacing for the hub is 135mm, everything on the frame is fine.

The cranks needs to come 'out' another 9mm, I think the only way is a longer bottom bracket. It's a pub bike, I'm not buying new cranks for it.

Assuming a reasonable margin of error on those measurements, it sounds like your crank is designed for a 120mm rear end, hence finding a BB with a long enough axle is unlikely...
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Longest bottom bracket I can find is only 127mm.

I've heard of BB axles that long, but only in formats like ISIS, where the axle reaches further into the crank, or BBs intended for using normal-ish cranks on Fatbikes.

Looks sort of like this one.

http://i.ebayimg.com/t/40-TEETH-152mm-COTTERLESS-CHAINWHEEL-CRANK-SET-BLACK-SINGLE-CHAIN-RING-/00/s/MTA2MlgxNjAw/$(KGrHqZ,!qoFCTCs6(MKBQon4Qsc0w~~60_12.JPG

Finding a BB that solves the problem with those cranks on that frame if likely to take you more time, money and effort than giving up and asking people to rummage in their parts bin for

A Deore Hollowtech2 crankset and a used £10 Shimano external BB.

I've bought HT2-compatible chainsets (including BB and chainrings) from eBay for about £25 in the past, and you could probably sell the 'rings and chainring bolts to minimise the overall cost.