Fail2Ban - how to prevent my ISP IP dynamic get banned?

fail2ban don't allow you to use wildcard addresses.
You have several possibilities :
1. use a dynamic DNS for the address you want to exclude
2. write an accept rule for iptable, executed prior to fail2ban rules
3. just configure fail2ban

How to configure fail2ban to ignore your address ?
Inside /etc/fail2ban/filter.d/ you have pre-made filters. Your rule(s) already use one of them (for example with filter = sshd use the sshd filter).
Just modify the filter(s) you want (or modify a copy) to add an "exclude" rule.
The exclude rules start with ignoreregex. They are written exactly as the "match" rules. Have a look at man fail2ban-regex.
For your example you can just add ignoreregex .myISPName.co.uk in the desired filter.
But this will also protect any attacker from the same ISP.