How much would you offer on a house on sale for £185,000?

20K less will not be accepted. the price is taken from comparables which have recently sold in the area.
You can put in an offer for whatever you want, they can only say no. I would expect they are aiming for 180K or maybe a little less.
Any house is only worth what someone wants to pay for it,
And No --Surveys are not done in England until an offer is accepted.

former Estate Agent UK

Strangers on Yahoo from all over the world have no clue how to value the home you're looking at. This is what a proper estate agent is for.

I would ask the agent or look at online resources to see what percent of asking price most homes in that area are selling for. In my area, homes generally sell for 95-97% of asking price, so even an offer of 170 would be too low. You can offer whatever you feel is fair, they can always turn down your offer. If your offer is too low, they may not even counter, they may just turn it down flat and reject any future offers from you, so keep that in mind.

You can offer what you like.
The risk is with a new to market property is they will wait and you can lose to a higher offer.
If another viewer likes it better then can offer the full amount.
I have seen a full offer got in 24 hours.
It depends on who is buying and how good the property is.
£170000 last year but what condition and how have prices changed in your area.
A house oposite me sold for a low price last year. They are still sorting it out.

if a comparable but larger one is on the market but has not sold, you might offer 20k less and see how this goes with the seller

Have you viewed it? If so do you know a builder who could go around with you ( with a professional eye and a lot cheaper than a surveyor) who will give you a first option. once you offer and it is accepted that is the time to have a structural survey, especially as it is over 10yrs old, under that and you have the builders insurance cover
Do you have your mortgage in place ?

No one can tell you what to offer, no one knows where it is, take no notice of zoopla they guestimate based on many things and exclude many other things, just playing around having signed into my property on zoopla, I use rooms in it one as a very large study, it could/should be a large double bedroom another as a second lounge again it could/should be a large double bedroom, so 4 bed/ 3 reception or 2 bed/ 5 reception rooms £200k difference in price of the same property, no where on zoopla does it account for acreage of land, so 7 acres of land ( which it has) or a postage stamp garden would be the same price, no where does it have other buildings or 'facilities' such as a menage, stables, fill sized indoor centre so it doesn't add cost for those, so the price they have is far short on reality.
Just remember a local professional estate agent has valued it, they are rarely wrong on reality of price, of course there is some room for maneuver BUT that will depend on the seller and why they are selling...can't afford to keep it they will want to sell and may drop more than someone 'needing' x amount to purchase their next property which might be twice the price or trading down to be mortgage free, so depends, one thing you do not need to do is upset the sellers as sellers as silly as it sounds (but is human nature) like to sell to people they like, my gut instinct is you will get it for no less than £10k cheaper and more likely much less than that and you only need two people interested and it will will be sold much higher than what is the advertised starting price especially in that price range

You can offer any amount all they can say is no. Offer a bit more until you reach a happy medium

The home report will tell you its true value, so will a surveyor's report
So base your offer on that along with knowing who else is interested in the property
If there is a lot of interest, then the price will rise
If there is little interest, then you can offer the price as stated in the home report or surveyor's report.