The advice is contradictory?!

[PoptartPoptart]

They need roughly 60% of the population to catch this virus so we can develop a herd immunity, yet they are telling us to wash our hands to reduce our risk of catching it or passing it on??
So is the hand washing mantra just a bid to slow the inevitable spread, rather than to genuinely stop people getting it and passing it on?

Yup, that's it. It's to stop the health services being overwhelmed by everybody getting it at once. Which is what's happening in Italy.

Winter is a tough time for the NHS anyway, the pressure is less likely to be lethal in summer.

I would imagine (although I am by no means an expert) that the assumption is that the spread cannot be stopped. But, by encouraging washing hands etc it can be slowed down so fewer people have it at the same time. In the end the result will be the same (ie enough people will have caught it to result in herd immunity) but you won't have a huge surge where loads of people get it all together and society can't cope - nhs can't deal with all the cases requiring medical attention, too many people are off work at once etc.