Every new car seems fractionally larger than the model it replaces – a trend that is having a profound effect on the marketplace.

The current Volkswagen Polo is now the size of a 1974 Mk1 Golf, superminis are attracting small families and medium cars are so TARDIS-like inside they sell to those who would have once only bought big. So buyers can effectively downsize without, er, downsizing, because there's as much room and kit in a modern, say, Toyota Corolla, as you used to get in a bigger car.

The losers are cars like the Mondeo, Vectra, and especially, the Vauxhall Omega, so anyone in the market for one will bag a bruiser for a real bargain. A year-old Omega 2.2 saloon can be bought for under £10,000.

Mid-spec 2.0 Zetec '00 Mondeos are currently around £7,000 in a private sale. Vectra is even better value – expect to pay about £5,200 for similar age and spec.

But buyers at the luxury end of the market can really take their pick. Most new sales are plush 4x4s like the BMW X5, Mercedes ML and Mitsubishi Shogun. The used market is now awash with bargain-priced Lexus LS400/LS430, BMW 7-series and Mercedes S-class.

Such models may lack the sophistication of communication packs, sat-nav and TV but still have climate control, electric adjustable seats and leather seat trim.

Cars with mileages over 80,000 are again struggling to find buyers. Just when the trade thought it had overcome the high-mileage stigma, it seems no-one wants them. Mondeo, Vectra, Laguna and Passat are worst affected. A high miler with full service history could prove a great buy.

More buyers are demanding air-conditioning on their next used car and the good news is that there will be many more of them about this year. Air-con has been standard on many lower spec models for the past three years and these are coming on to the market now.

Benchmark cars with air-con such as Peugeot 206, Vauxhall Astra Club, Ford Focus Zetec, Citroen Picasso LX/SX will become more widespread, but less fussy buyers will find bargains on similar models lacking the facility.

Audi TT values are starting to drop due to the obvious weight of numbers. The 225 coupe is more desirable as it costs little more to insure than the 180, which can be had for £10,000.

BMW 5-series models – 1996-on – are making a comeback. These suffered a decline in price over recent months and now look good value. The 520/523 models with leather interiors are good news and 525tds are also the target of keen buyers.

Ford Ka continues to amaze – used stock seem inexhaustible.