As of 2017 we [Brits] spent about 5.6 per cent of national income on benefits for those in old age against 7.1 per cent in the US, 7.7 per cent across the OECD as a whole, 10 per cent in Germany and more than 13 per cent in France.
And yet the country is still in economic troubles. In any case, that is from the new and excellent Paul Johnson book Follow the Money: How Much Does Britain Cost? This book talks you through both the tax expenditure side of the British government budget. It is not quite thrilling, but given the topic area it is remarkably interesting and well-executed. And while the authors is not without his own ideas, the book is more to inform you than to propagandize you.
You can buy it here. There should be many more books just like this one, but for different topics — take note!