OP, Quin is right, realistically, you need £30k more for the same standard of living as most of continental Europe.
We are a family of 2 adults, one 4 year old and a baby (who is FF), we spend £120ish a week on food/cleaning products, we meal plan and probably could get it lower, but are by no means excessive in what we buy. I assume you've come to the figure of £600 by looking at somewhere like Sainsburys website and pricing up your current shop. Realistically, a UK move will require changing/downgrading the way you eat as well as live.
But, if you have a family draw to the UK (or just would like to be back here), then it's doable on £40k (plus CB, think that's all you'd be entitled to, but as I said earlier, that's an extra £150 a month if you have 2 DCs, so your sums would add up, and I think you could probably get car and home insurance cheaper).
I would look at you working to, apart from anything else, for the pension issue.