So you haven't actually got a sealed offer on your flat yet? Stop putting offers in on other properties, it means nothing and will just lead to more heart-break
Absolutely spot on. Until you sell yours and have a complete chain behind you then you are not proceedable. The estate agent will call your agent to confirm the chain is complete and qualify your offer.
You could offer 3x the price of the house you re interested in but it counts or nothing.