Thanks for the replies guys, I have had a look at mine this evening (took a bit as been away) and I think I have 25mm on the back, but in fairness I measured using a key and then measured the key when I got inside, so they might be 20mm 🤣
Can I assume that 20mm will be alright for the front even of running 25 on the back?
Note that tyre sizes are standard 285/19 on back and 245/19 on front 👍