Nearly got all the parts needed for a complete refresh of my suspension on the Fabia, just need to get the bushes and I'm ready to go, I've decided to buy the SuperPro KIT5229K. It is supplied with 20mm anti-roll bar bushes, I have checked the bar on my car and a 20mm spanner went on the bar snuggly, am I correct in thinking that the supplied 20mm bush is fine or does it need a tighter fit therefore requiring me to request the kit be supplied with a 19mm bush?

The bush itself will not be 20mm, it will be sized for a 20mm ARB, which is what you have. So...