I P/ex'd my 7 y.o. Citroën Picasso 2.0 HDi for a 2007 Škoda 1.9 TDi ex demo with 11k.

I religiously changed the oil and filter on the Citroën every 10k and used fully synthetic Total Quartz 9000 throughout. The engine used no oil between changes and ran sweetly for all of its 96k. - The Picasso was a blooming good car, very little went wrong.

The Octavia is set up with variable service intervals so I've no idea how long to run with the oil and filter, nor any history of what oil to use.

It hasn't used any in 1500 miles.

Any advice please?

If you haven't got any service or driving history for the Skoda then it may be prudent to assume that it has been driven for short trips and needs an oil and filter change. For a TDI I would use VW 507.00 spec oil (but be warned, it is usually a bit expensive).

The variable service can go up to 20,000miles/2 years, but that is a bit too long for my comfort and confidence levels, especially on a diesel.

You manual should describe how to display when the next service is due (IIRC it involves switching the engine off and pressing the trip meter reset button for 2 secs or something, but that might be totally wrong).

I would do oil changes at 10k myself and full services at 20k.

Mainly because I've noticed a huge difference in the smoothness of the engine when changing oil at 10k.

Also worth doing the air filter every full service rather than every 40-60k miles.

As above if there is no history I'd assume nothing and have a service done early if you intend to keep the car. Better to lose up to 5k on the service than to have to spend out later because a previous owner has added a lot of the wrong oil as top ups.

Its not that old so keeping it service by your dealer or an independant is essentail to keep your warranty and will help the resale value.

Personally I would service it on 10k/12 months also if it was mine. Just makes life a lot simpler.