"If these restrictions fail to bring the R number below one - the point where the epidemic is no longer growing - "then we reserve the right to deploy greater fire power with significantly greater restrictions" he said.
Mr Johnson said: "We will spare no effort in developing vaccines, treatments, new forms of mass-testing but unless we palpably make progress we should assume that the restrictions that I have announced will remain in place for perhaps six months."
Under the new measures:
- Penalties for not wearing a mask or gathering in groups of more than six will increase to £200 on the first offence
- From Thursday, all pubs, bars and restaurants will be restricted to table service only. Takeaways can continue
- Hospitality venues must close at 22:00 - which means shutting then, not calling for last orders"
- Office workers are being told to work from home if possible
- The planned return of spectators to sports venues will now not go ahead from October 1
- Face coverings must be worn by shop staff, taxi drivers and passengers
- Customers in indoor hospitality venues will also have to wear masks, except when seated at a table to eat or drink
- Exemptions to the "rule of six" will be cut back, meaning indoor team sports such as five-a-side football matches will end."
"Mr Johnson said this was "by no means a return to the full lockdown of March", with no general instructions to stay at home. Businesses, schools, colleges and universities will remain open."
Increased fines for rule breakers and limits on wedding numbers are among the new measures in England.
www.bbc.com