Legal according to who? You seem to forget that the head of the Polish Government in Exile, Stanisław Mikołajczyk, considered the government in Poland to be the legal government and that is why the London Poles replaced him as Prime Minister of the govt in exile.
Can you state the quote?
Nothing like that appears in 'The Pattern of Soviet Domination' by Stanislaw Mikolajczyk, London, Sampson Low, Marston & Co.,Ltd. 1948.