You can put an offer in whenever you like. But the seller is under no obligation to stop carrying out viewings / consider any others that may be more proceedable that may come forward in the time you take to sell. That's assuming they accept your offer at all.
We're in a similar position having seen a bigger property locally that we keep debating going and viewing but haven't even had ours valued yet. It's the first time we've seen a property of that size vaguely within our budget and just keep umming and aahing over whether to take the plunge and start the ball rolling!
You can offer but most vendors will tell you to come back when yours is sold. They may well instruct the agent not to take offers from nonproceedables! We turned the people who bought our old house down initially because they had not sold, they came back when theirs was sold and we accepted the offer.
I do sympathize, I fell in love with a house and made an offer, vendors told us to come back when ours was sold but they received another offer and we lost out before ours sold. BUT we then sold and found this house which is my dream home and much better. it will work out in the end.
I am in Reading so am intrigued which one you really like! PM me a link?! We just accepted an offer on a 2 bed terrace in west reading after 10 days being on the market so you could sell quickly too?! Time to get decluttering like mad!
Ive bought and sold many over the years and one thing I have learned from that is that another house will always come along! Its hard when you have set your heart on a place but you will probably find a better one and be glad you didn't buy the first place.
How about putting your house on the market with the same EA as the house you love - that should motivate them to sell yours, and also if you get an offer say £10k lower than you want/need, they will be motivated to get the other house for you £10k lower. Worked for us.
What Sunny said - we did exactly the same. Our EA managed to negotiate the price drop off the whole chain - we took a bit hit on our house at the bottom of the chain, but they persuaded the people at the top that it was a teeny percentage of the full value of their house.
I wouldn't recommend putting in an offer before your house is on the market though. People are funny - a house can sit on the market for ages with no interest, once one person puts in an offer, other people suddenly see it as desirable and are more likely to put offers in. Don't show your hand too soon.
Other houses will come along if this one is snapped up. 1 in 3 sales in Reading fall through at the moment (according to my agent). If they place you like does sell, let the agent know that you would like first refusal if it comes back onto the market. That's what we did - many vendors would be delighted to not have to bother tidying their house for viewings again if they lose their original buyer.