Divorce proceedings have now changed (from 6th April 2022). The first stage no longer has to be issued by one spouse, they can make a joint application if they wish. This clearly removes the element of blame involved as in previous divorce law. No one has to say what caused the marital breakdown, just that the marriage is over. It allows couples to split amicably.
The law demands a 20 week period of time from application to the issuing of the conditional order (previously called decree nisi), and then a further six weeks until the final order (decree absolute). Therefore it will take at least six months for the divorce to go through from start to finish (all things being equal - financial proceedings could delay this).
The biggest change is that you can divorce without blaming the other party - only one person needs to provide a legal statement to say the marriage has broken down irretrievably, and this statement is conclusive evidence and cannot be contested. The application costs £593.
If on a low income/benefits, fee remission may be available.
Form D8: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1064336/D8_0422_save.pdf
Online system: https://www.gov.uk/apply-for-divorce
EX160 form: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/952045/ex160-eng.pdf
More info on the process: https://www.gov.uk/divorce
Online fee remission: https://www.gov.uk/get-help-with-court-fees
You can find an authorised and regulated solicitor here: solicitors.lawsociety.org.uk