Section 14 of the Supply of Goods and Services Act 1982
requires services being provided by a business to be provided within a reasonable time unless the contract or dealings between the parties provide otherwise.
I doubt that anything in the contract sets a date for service provision that would be extensible to 8 months, and an 8 months delay is clearly not reasonable.
A more detailed analysis of the scenario will likely reveal that Virgin Media have breached the contract by their failure to provide the contracted service within 8 months, and this breach would be such as to entitle the original poster to breach of contract. However, that argument is more difficult to make out for someone lacking legal experience, so it's probably easier to try an argument based on s. 14 SGSA 1982 first.