We don't have a 45 degree downwind join in the UK.
Is there any rule or law forbidding it? Please quote official source?
Or is there a list limiting the ways one can legally join the circuit? Please quote official source?
In this case it is clearly the AIP for that airfield: overhead join at 2000ft AGL descent to 1000ft AGL is published as VFR procedure. (And ATZ is 2nm around the field, so 4 nauticals is Lord Farquart ... far far away kingdom.