Is 140kWh of gas a day normal?

Verdigris

If the house had been unheated for a while and you've only moved in very recently, it will take some time for the thermal mass of the house to stop absorbing heat, until it is more-or-less in equilibrium with your desired room temperature. The consumption should go down once the walls has warmed up.

I had the very starkly illustrated when I lived in a large house, with 600mm thick solid stone walls. After a big storm, in the early 1990s, we had several mature trees, including a 30 metre high Monterey Pine, on their sides in the garden. I decided to put this to advantage and fitted a wood-burning boiler in parallel with the existing oil boiler to get some "free" heat. At the start of each heating season I was barrowing-in logs 4 or 5 times a day, to feed the beast, but after a week or so suddenly only one or two barrows per day were required, once the "storage heater" of the building fabric was up to temperature.