I have family working in the pharma industry, and work contacts in pharma at Oxford. Whilst the NHS/Army might be ready to start vaccinations in Dec, I'm afraid there is no chance the vaccine will actually be ready by then.
The best guess is that they may be ready to start the vaccinations in late spring-early summer 2021(April-June). Even once a vaccine is approved, you've got to produce 68 million doses for the Uk, 500 million for greater Europe, similar numbers for North America etc. It takes about 3 months for the NHS to administer the flu jab, and that's typically only 15 million doses.
The next issue is that it's looking increasingly likey that the Oxford vaccine has some significant side effects in up to 70% of patients. Also, it's not 100% effective (I've seen 70% quoted), and will probably require a booster jab after 6 months as well, this doubling the number of doses and work required. Herd immunity won't start to take effect until 50% of the population are vaccinated, and the risk won't drop to 'acceptable' until 80%+.
Put simply, I wouldn't be too confident of things being back to near (new) normal till this time next year.