Virgin Media are currently offering the above SIM Only deal for £15 on their website but I called them on 0800 052 0422 and asked for 6 months half price. The gentleman over the phone was more than happy to offer this to me so took out two contracts with him for myself and the mrs.
After the 6 months, it will go back up to £15 but I am not tied to any contract and can leave anytime. I can also confirm that I am a new customer moving from the Three network. If they don't offer you this at first do try again, but using that number. They wouldn't offer this to me over chat.
The £15 deal ends on 31st January so I would assume this £7.50 offer is available till then but I'm not sure.
Tariff: Virgin Media SIM Only 20GB Tariff
Minutes: 5000 Minutes
Data: 20GB Data
Texts: Unlimited (standard UK SMS)
Features & Benefits
Free messaging on WhatsApp and Facebook Messenger
Change your 4G plan up or down every month
Keep Your Mobile Phone Number
Free WiFi at 250,000+ hotspots
Hope this helps someone! (Have attached email as proof of purchase)