Tap Connector Query

These reducers are very common, I'm surprised you were not able to find one. The push fit connector usually comes with an adapter bushing for this purpose.

Bring the removable part to a plumbing supplies and see what they can do for you.

OP there is a simple answer that is don't do it. ;-)

Here's my suggestion. Cut a length of hose that nearly touches the ground. Attach that to your original barbed tap connector on the other end attach the hose to hose connector.

That will leave you with a flexible pipe left connected to the tap which is ideal for filling watering cans. Connected the full length hose to the end of that when required.

That's true, op's thread does look different though.

Anyway your idea above is the best solution.

You can still do all that. Once you attach a hose end connector to the hose you can then attach one of these which turns it into the de facto tap end.

The sizes are nominal or should I say notional its related to the bore of the pipe not the outside thread of the fittings. That isn't a 1.25inch fitting its a one inch fitting at most. Problem is from what I can see its slightly bigger than I'd expect of a 3/4 inch fitting and a tad smaller than a 1 inch?

See if you can accurately measure that outside diameter of that thread in mm. I've just measured a few 1 inch fittings and they measure between 32 and 33 mm across the widest part of the thread.

New taps aren't 22mm at the hose end they are all still imperial but at least you have worked out what the problem is. I suspect the 3/4 marked on the tap is the fitting to the mains pipework not the hose fitting.

If you want to hunt down a fitting this might help seems there is an inbetween size

https://www.stevensonplumbing.co.uk/7-8-outside-tap-connector.html

but a new tap will be cheaper and quicker. If you can take the old tap with you to the builders merchants (should be cheapest) just to be sure you get one with the same fitting for the wall but 3/4 inch is fairly universal.

A bit more expensive but I started using these for outside taps, no problems since with freezing up in the winter

https://www.plumbingproducts.ie/valves/5335-philmac-hose-union-bib-tap-25mm-34.html

If the OP is up North anytime soon?

https://www.raygrahams.com/products/157464-brass-farmers-tap-connector.aspx

And found an adaptor (new tap is cheaper) and explanation

https://www.access-irrigation.co.uk/shop/pipe-fittings-taps/pipe-fittings/threaded-fittings/7-8-3-4-threaded-adaptor/