[neil_s_wood]

I find different manufacturers vary considerably in running quality. Hornby tend to be the worst as they have weak motors and very little weight to give traction. I find Bachmann a lot better as they have more weight. Continental and American models are a lot better than either as they are far heavier, although the RP25 wheels on American ones generate more derailments. Trix, which are my favourite German trains, derail very rarely. This could be due to their wider flanges on their wheels as well as the fact that they have metal bodies which increases the weight.
Some of the recent Hornby ones such as Duchess and Princess derail almost constantly and I now only really use my Hornby locos as display models as the running quality is so poor on some. Some aren't bad like the Merchant Navy class but I find most Hornby more trouble than they are worth.
The American ones tend to have good traction when they are on the tracks but due to the shallow flanges they tend to derail when they go over points. So you really have to do a lot of test runs to see what they will and wont do.
I forgot to mention Lima, who are far worse than Hornby. The running quality on them is so bad they can only be used as static models. I think this is due to the lack of electrical contacts on the wheels.
I don't think modern models are any worse than older ones, but if you only buy UK models most of whats available is poor. Have a look at the running quality of some of the German locos and you may be surprised at whats available now.

 

[neil_s_wood]

I would agree with the above, all the problems I have had with derailments with Hornby steam locos are due to the front pony trucks. What solution did you find to resolve this?

 

[neil_s_wood]

QUOTE maybe we will see cast metal boilers on the likes of Hornby and Bachmann in the near future.

I really hope so. It would give them the extra traction they need.