Does anyone know where I can get a Oxygen bottle refilled (Beergas)

Or know a friendly landlord that might swap an empty bottle for a full one (paid of course).
Not too far from Essex would be a huge plus.
I have a Mig, it came with a 'empty bottle'. I know I can buy the Halfords disposable ones, but would need to change over the connectors, and I already have valve and Gauges.
Any ideas, last time I welded was about 1980

so a bit out of practice. Really don't want to invest too much as want to have a go before blowing holes in my 126's floor.