Figures from Britain's two biggest lenders, Nationwide and Halifax, will point to falls of around 1% on average property prices across the country over the past three months, pushing values roughly back to where they were a year ago.

But prices are already tumbling in some areas, with prestigious new developments badly hit both by sliding values and rising repossessions. Agents are reporting growing numbers of purchasers of riverside luxury apartments in particular handing back the keys and walking away, depressing prices further.

Five repossessed apartments on Edinburgh's waterfront went under the hammer last week at an auction organised by Countrywide Property Auctions in the Quality Hotel, Glasgow.

A three-bedroom repossessed flat in the luxury waterside development was advertised with a guide price of £125,000 and fetched £170,000, even though similar properties are currently for sale from £225,000 to more than £500,000.

Two-bed flats were put in the auction with a guide price of £120,000, with one reaching £160,000. Sellers on the open market are asking around £225,000.

The Property Snake website is currently advertising flats at the waterfront developments which have been on the market for up to 40 weeks, and have slashed their prices by up to 35%.

A spokeswoman for Your Move in Edinburgh's Leith Walk said: "Unfortunately, we are seeing a lot of repossessions coming on to the market in this whole area. As prices fall, people realise they are facing negative equity and so the temptation is to walk away.

"A great deal depends on what kind of deal they got when they bought. Although the prices fetched at the auction were lower than these units were marketed for when they were sold, some people received substantial discounts and cashback deals. It is difficult to know how much they lost on the transaction without knowing the size of an individual's cashback.

"However, sellers are becoming more realistic and they realise they may have to accept less for a property than they paid."

According to Edinburgh Solicitors Property Centre, the number of properties on sale has increased by half, while completions have tumbled by a fifth. Unusually, more than 60% of sellers have moved to a fixed price, indicating that they are struggling to dispose of their homes.

At the end of March, Nationwide indicated Scottish prices had fallen by a negligible 0.1% over the previous three months, and Halifax estimated they had risen by 0.2%.

HBOS chief economist Martin Ellis said: "In other words we both felt prices didn't move between January and March, but the market has deteriorated since then. We expect Scottish values to fall over 2008 – although not by as much as some areas south of the border – and end the year lower than they began it."

Nationwide is expected to announce that average Scottish house prices are now around £148,000, while the Halifax will put them closer to £143,000 when it publishes its second-quarter statistics.