No, existing petrol cars are not being banned and there are no plans to do so. In the UK, the government has stated it intends to stop the sale of non-hybrid petrol and diesel cars by 2030, and outlaw the sale of fuel-powered cars altogether in 2035.
You will still be allowed to drive your petrol car in the UK beyond this point, but you won’t be able to replace it with a new one.
What might change over time, however, is the cost of entering and parking in cities. Several large urban areas in the UK have already introduced low emissions or clean air zones, which apply a surcharge to older, more polluting vehicles. Over time, the definition of which cars will face this surcharge could change, meaning your currently compliant car might one day incur an extra daily cost if you want to visit the city centre.