If it happens next week, a 5 December election becomes the most likely option.
:: 31 January
This is when the EU is likely to extend the Brexit deadline until, although this is not guaranteed.
Three months is what Mr Johnson requested, in order to comply with the so-called Benn Act.
This is the legislation passed by MPs to avoid a no-deal exit on 31 October.
A senior EU source has said that European Council President Donald Tusk will recommend that EU member states accept an extension until the end of January, which can be terminated when or if a Brexit deal is ratified.