I echo what the others have said - we actually went to a solicitor as we separated, and took out a separation order, to make it clear who was responsible for what during the period we were first apart. That document made the date of the formal separation clear, and meant that two years afterwards, divorce could be filed for on the grounds of the breakdown of the marriage. He didn't contest - but if he had, I would have had to have waited another three years to resubmit the papers. There is no dissolution of the marriage automatically without going through yoru local court process.
Yes it cost for the paperwork, but in the end, it saved a lot of potential problems as everything was clear cut from the day I left.