what is a reasonable offer?

[narna]

have been to view a house priced at 135 k. It is a repossession.
Having no experience with buying houses,me and DP are a bit lost as to what would be a reasonable offer.
Any help would be much appreciated...

Have a look on housepricesuk or zoopla to see what it was bought for. (may be in negative equity which is harder to get a deal on)
Start low and work up, but at least 10-15% under.
Once you put an offer in, if it is refused the estate agent may give you a hint as to what it needs to be.
Don't forget once they accept though it will have to have a public notice in the local paper and someone else could come in and offer above you right up to exchange date.
(Have bought repos before so as away if you have any other queries!)

aim for your first offer to be rejected for being too low. If they accept straight away you will kick yourself for thinking they might have accepted even less. Like Jack says, 15% under which would be £115,000 for starters. But expect this to be rejected and for you to have to haggle upwards. I think on average houses get something like 94% of the original asking price. But that's an average!

What are other similar houses selling for in your area? Check using the websites jackstini has linked to as this will give you the selling prices, not the prices they were marketed for.

Does it need any work doing to bring it up to the standard of the houses you're comparing it to? Factor those costs in and also allow something for the distruption and hassle you'll have in doing the work.

How long has the house been on the market and quickly does it need to be sold? The company who repossesed it probably want shot of it as quickly and easily as possible so make a big thing of how quickly you can proceed. First time buyers (no chain) are reckoned to be worth a couple of thousand off the price. If you're a cash buyer (no mortgage) then you should be able to push for a bit more off the price.

always at least 10% below the asking price as an opening offer. At least.

It will depend on your position, really. If you are good to go (first time / in rented) they are more likely to accept a low offer as they know they will get their money more quickly than they would if you were in a huge chain.

That said, they are legally obliged to get as much as possible for it so any opening offer is likely to be rejected, on principle.

Talk to your agent and say that when they put the offer forward it is made on the basis of "nothing to sell, work needs doing to it" type comments.