Ian, here is my original plan that I stuck to. The car runs very well. I am a sceptical, scientific kind of a guy so I made my own decisions based on a lot of reading. I suspect the topic is like Marmite: there are those who say it is necessary and those who say it isn't. The problem is that if there is a case for a certain style that gives better long term performance of the engine it would be difficult to prove by the average car forum member. So being cautious, this being my first new petrol car and thinking I would keep it a long time, this is what I originally came up with and followed pretty closely.
I've been doing some research on running-in modern engines. There are a variety of ways to do it but I've decided to put together my own hybrid plan. The key part is bedding in the piston rings as early as possible, without straining the engine. This is done in the first 20 miles if possible. Other than that I don't think there is much controversy, although opinions range from "run it hard" to "be gentle"! This applies to petrol engines but the principles are similar for diesels (my previous new car was a diesel).
Here are some of the sources I used:
Mototune Break In Secrets
PistonHeads Forum Running in a new engine
SEAT Arona Owner's Manual
This is my plan:
Overall, vary the revs and do not sit at a constant speed for long when running in.
From new with a warm engine and as early as possible, within first 20 miles,
ideally 
(you need a long, straight, quiet piece of road):
- Stage 1, 5 times (50% throttle):
In 3rd gear, accelerate from 1500 rpm to 3000 rpm, lift off pedal, let engine braking take the speed back down.
- Stage 2, 5 times (70% throttle):
In 3rd gear, accelerate from 1500 rpm to 3000 rpm, lift off pedal, let engine braking take the speed back down.
- Stage 3, 5 times (70% throttle):
In 3rd gear, accelerate from 1500 rpm to 4500 rpm, lift off pedal, let engine braking take the speed back down.
Within the first 500 miles, if you get the opportunity to repeat stage 3 above, do so.
First 200 miles:
3000-3600 rpm max, 70% throttle, never full throttle
200-500 miles:
3000-4500 rpm max, 70% throttle, allow full throttle further up the rev range (i.e. when in a lower gear)
500-1000 miles:
5100 rpm max, full throttle further up towards max revs
1000 miles on:
Normal driving
SEAT Owner's Manual Advice
First 600 miles
- Do not drive at speeds of more than 75 mph.
- Do not accelerate hard.
- Avoid high engine revolutions.
- Do not tow a trailer.
From 600 miles to 900 miles
- Speeds can be gradually increased to the maximum road speed or maximum permissible engine speed (rpm).
During its first few hours of running, the internal friction in the engine is greater than later on, when all the moving parts have bedded in.