When I bought recently, the property was marked SSTC after the Memorandum of Sale was completed and issued.
For the Memorandum of sale to be issued, which is basically written evidence of the offer, you need to have supplied as buyer evidence if funds (evidence of deposit/funds and mortgage offer if you need one) and have appointed your solicitor and that’s been confirmed. They will also need to do identity checks so get all your paperwork copies of passport etc in. Naming the surveyor you will use also helps. Many people won’t book the surveyor to actually go until the property is marked SSTC and that’s reasonable.
The Memo Of Sale is shared with the seller and buyer. It means you’re officially proceedable and lots of EAs won’t remove property from market until that is completed. Too many people make an offer and then it turns out they don’t have the finance in place. They might say they’re a cash buyer, but when asked for evidence of funds it turns out they aren’t. Or they can’t get a mortgage, or they drag their heels to appoint a solicitor.
The key for you as buyer is to provide these things ASAP. Some people give them to EAs before making an offer to show they are serious buyers. Others deliver them on the day they make the offer.
If you are seriously house hunting and havent got this paperwork together, then do it now. If you don’t, the period when other buyers can look at the property is longer and there’s greater risk of a higher offer or better buyer in terms of oroceedability appearing. You can never guarantee until exchange a sale will go through and some sellers will switch buyer at any point, but many won’t after the ball is rolling and they’ve got the Memo of Sale and you’ve started forking out for survey etc.
Essentially, do everything you can to show you’re proceedable and serious. Dont just say it but evidence it with the paperwork. Realise gathering this stuff can take a while so do it before starting to look so you can drop it off at a moments notice as required. Remember often only hard copies will do and emailed versions won’t be accepted. Sometimes you’ll need to get things certified or witnessed so work out who will do that for you and choose people you can easily access. You do t want delays of a week because you can’t see the person who needs to certify a document.