Halfords Value 5 Function Cycle Computer is wired, with a universal mount for handlebar or stem. Features single button control to easily navigate through the five functions, including current and average speed, odometer and trip distance. Universal mount for handlebar or stem fits all bike frames. Cost £8.99
As you might easily become bored or frustrated with its limitations, I've included:
HALFORDS 8 FUNCTION CYCLE COMPUTER is wired with single button operation making it simple to navigate between the functions. Functions includes current, average and maximum speed, odometer, trip distance, clock, riding time and scan making this cycle computer a simple but useful tool for cyclists keeping an eye on fitness or with cycle exercise programmes. A wide range of cycle computers and accessories are also available.
Weather resistant construction, suitable for use in adverse weather. Universal mount for handlebar or stem fits all bike frames. Cost £12.99
12 hour clock
I don't actually have any of these, I was only searching on-line for one and found them straight away, so I can't say whether they are reliable/durable, etc.
Trial and error is the best way to find out, anyway . . .