Was the decline of the British Empire a decisive factor in the South African elections of 1948?

Out of the Dugout Questions
1

Was the decline of the British Empire a decisive factor in the South African elections of 1948?
The margin of victory for the National Party was very mall and the National party only won because of the first-past-the-post electoral system, while the United Party of Jan Smuts got more votes than the National Party of Malan.
Every minor influence might have been decisive.
Why was the beginning of ‘Apartheid’ not mentioned in the 1948 Newscass W2W 26?