Being honest, the lowest you’ll find for applying to Russell Group is AAA. You can sometimes get lower with either an EPQ grade A in law/legal topic (usually AAB if usual offer is AAA), OR if you’re eligible for a contextual offer. I’d check that out on the various Uni websites.
Some RG can sometimes be in clearing eg Liverpool with AAB/ABB but no one knows how that will be until results come out.
Don’t forget unis like Lancaster who aren’t RG but gave quite a good rep for law.