This is a fairly recent development. Before 1980, Singapore imported its textbooks and relied on English examination boards to set its secondary school curriculum. Many people have argued that the English GCSE Maths syllabus has become easier over the past 25 years, whereas Singapore's O-level has retained its rigour. Certainly, UK schoolchildren do not compare well to their South-East Asian contemporaries in any study I have seen.
Of course, the National Curriculum is not the only game in town for English parents. There is also the Common Entrance Exam, which is a superset of the National Curriculum intended to stretch the 7% of children who are competing to enter elite private schools at 11 or 13 years of age. Still, the syllabus for 13+ Common Entrance is a pale shadow of the one used for children in Singaporean schools.
UK politicians have noted these problems, and Michael Gove has made encouraging noises. However, he stands little chance of success as there is no cross-party agreement, and the teaching unions will oppose any change to the status quo. There is an argument that making Primary Maths more difficult will unfairly benefit children from wealthier backgrounds, and will discriminate against families from the North of England. Unfortunately, that's an argument against any form of education for children, which will always benefit those with supportive families.
One of my friends has a very sensible attitude towards national politics, which is that he forces himself not to care. The only thing that matters is his family, and if his nation wants slowly to destroy its children's education, it's not his job to stand in the way. It sounds defeatist, but if parents want their children to receive a decent standard of Maths education, it will have to take place outside school.
My daughter is about to reach the age of four, and it seems like the right moment to make choices about her education. She's already started a phonics course, and we'll start handwriting practice in earnest in a few months. I've also decided that she should try to keep up with Singaporean children her own age. This means half an hour a day, five days a week of Maths study.
Reception Maths (age 4/5 years)There is a UK distributor of Singapore Maths named MathsNoProblem that stocks EarlyBird Kindergarten books. You only really need the two textbooks costing £22 each, but there are also optional activity books and 10 readers. The readers are only available from the US distributor.
The course uses a lot of material from around the house, together with some suggested manipulatives, which are available from Amazon: multilink cubes, various counters, a hundred board, a simple balance, and a clock with geared hands.
Grade 1 Maths (age 5/6 years)The first year of Singapore Primary Maths 3rd Edition textbooks and workbooks will cost £42. Make sure you get the 3rd edition, not the US or "Standards" editions, which use American units and spellings. There are also a lot of manipulatives that need to be bought. To be honest, it's cheaper to order the manipulatives from a specialist home-school supplier in the US such as Rainbow Resource Center. There are also additional resources available, such as the Extra Practice and Challenging Word Problems books.
After the first year of Primary Maths, it's worthwhile buying the Home Instructors' guide, or the more expensive Teachers' Guide, to help you plan lessons.