Sorry, Kev, my reply should have referred to your 1/2 tank level at which you would refill in normal times - i.e. 45 litres. So taking 2 x 25 litres top ups in accordance with some rationing limits at fuel stations is in essence [no, not French for petrol ...]

refilling at 1/4 usage, with a 10% margin to cover the extra mileage if the less expensive fuel station is a little further up the road. It's also consistent with our exchanges 1-2 years ago about my habit of checking mileage covered at 1/4 usage stage to check that it's 130-140 miles because any lower distancecould indicate a developing problem with the engine/gearbox et al.
I'm not sure many of us get out much at present - the M/Home is used to run the induction hob for cooking to keep the new
lithium battery working, instead of sitting at float [also saves 2 pence on the household leccy ...]; and the car gets used once each week for shopping, with any top up supplies collected from Asda - a 1.5 mile walk [return], using the Pedal Power bike bags [like the TdF riders use to carry supplies to team mates] which will just carry a loaf each and a jar of coffee or similar. Good exercise to keep the hips from seizing up, and stretches the diesel for a wee bit longer ... 'First world critical survival tips' springs to mind
Steve