Measure the diameter of the pesky bolt you took out, or one of the other similar ones. My guess is it's an M6, Metric thread, 6mm dia. Measure length also, best measure one of the originals. If you can wait till Monday, you'll get one, and washers if required from Basingstoke Bolt & Tool, 1256 329781
Google Maps:
https://g.co/kgs/6LT3nJ
Minimum cash sale is £5. If I remember, they're male Torx. Take a good example with you, they're happy to help.
If desperate, Halfords probably have them in packs.
Mac.