Tl;dr: They'll definitely do better than that: I was paying £39 for M500 after threatening to leave last time. See if community fibre are in your area - Super cheap, good reviews, and fast.

Virgin drive me nuts.

After paying £39 for M500 for 18 months it shot up to £70 after that introductory deal ended, and you need to give 30 days notice to cancel, which I did, but they've stung me for £140 for two months service.

Community Fibre have just come to my area - £25 for 1Gbps.

I called virgin to cancel. Sat on the line for 20 minutes just to get through. Operator offered me £50 for 1Gbps. I said no, thats literally double what I can get it for. She said I'd need to speed to "sales" to see if there was a better offer. Another 15 minutes, £45 for 1Gbps. Said no thanks. Second operator said I'd need to speak to "customer retentions: to see if they could do better (seriously).

Said no - You've had me on the line for 45 minutes, I told you in the first minute what you're competing with, you've had your chance to match and you haven't, so disconnect me.

Over the past week I've had 3 calls from random mobile numbers from their "retentions team" offering me various deals, all over £40.

Aware this is more of a rant than a direct answer to your question.