A 2021 update on the below:
Driving ~7.5 miles @ 7.5mpl, £1.45p/litre, costs £1.45 each way, that’s £ 14.50/week.
A 2018 update on the below:
Driving ~8 miles @ 7.5mpl, £1.26p/litre, costs £1.35 each way, that’s £13.50/week.

A 2017 update to the below:
Now ~9.6miles, 7.5mpl, £1.18p/litre
= £1.51 each way = £15.10/week
A 2015 fuel costs update to the below:
7.7 miles, 7.7mpl, £1.08p/litre
= £1.08 each way = £10.80/week
2013…
I’ve said it before and OK, it’s not about ‘time’, or ‘cost’, but just for the record:
7.5 mile commute into Leicester
On Monday (sometime in 2013) my bike was in for an annual service – and when you commute by bike, everyday, through all seasons, take my word for it, it’ll need a good service!
So Monday I took the bus: Novel
It took a bus 55mins! (+10min walk), Tickets £2.60 x 2, week ticket £25
(return is £6 duh!), £100/mth
+patience
On Tuesday I thought I’d try the car: humm, sedentary…
Car journey took 29mins, fuel £1.32 x 2, £13.20/week,
£52.80*/mth +legal* £37/mth, total £90/mth
+ Car maintenance costs**
Back on the refurbed bike on Wednesday! Ah! You know you’re alive – energy!
Bike, 34mins, fuel banana 20p. £1/week, £4/month
+Bike maintenance costs**

So Car 29mins, £14/week +costs,
then Bike 34mins £1/week +costs.
then Bus 55mins £25/week +patience.
*7.5 miles, 35 mpg, £1.35/litre = £1.32 fuel (£52.80/4weeks)
Annual legal costs: tax £100, insurance £300, mot £50 = £450
**Car and Bike maintenance costs, no comparison at present but could be similar on average.
2015 UPDATE : 7.7 miles, 7.7 mpl, £1.08p/litre = £1.08 each way = £10.80/week
2017 update : Now ~9.6miles, 7.5mpl, £1.18p/l = £1.51 each way = £15.10/week
2018 update : ~8 miles @ 7.5mpl, £1.26p/litre, costs £1.35 each way = £13.50/week.
2021 update ~7.5 miles @ 7.5mpl, £1.45p/litre, costs £1.45 each way = £ 14.50/week.