3 gas canisters put enough in my rear tyre to get me the admittedly lowly distance of about 3 miles to the nearest air line.
Unless I were making progress I doubt I would know if it was that low on pressure and I would happily have ridden at most speed limits apart from 70 for about 10 miles.
Richard had a rear that was so low I had to pull him over as I could 'see' how flat it was. He sheepishly said he did wonder but he sure as hell didn't pull over yelling 'I've got a rear puncture!'
Almost nowhere in UK is remote enough to worry. I now carry a compressor when on tour but my normal kit has four canisters now.