He railed, as the bullets tore into the unfortunate construction, against those who would deny a good Afrikaner the right to travel freely in the land of his birth.
That was in the mid-Eighties, when he was still an MP for the Afrikaner nationalist, right-wing Conservative Party (CP). Today, as energetic as ever but politically more mellow, he is an 'independent', having quit the CP in April over the the leadership's refusal to adapt to the negotiating times. 'Koos', as he is affectionately known, has travelled a long way.
In 1982, he stormed out of a meeting of the ruling National Party (NP), shouting: 'I'm finished with that bloody progressive P W Botha.' Others followed him and that day the party split, leading to the creation of the CP.
Now he is a De Klerk man in everything but name. He has the directness of the right-winger without the dreamy fanaticism, and the pragmatism of the NP without the instinct to dissemble.
'I went to Andries Treurnicht (the CP leader) three years ago and told him I couldn't stand this split between our people. So I went and talked to a number of cabinet ministers, and I realised that all Afrikaners wanted the same thing, the best for our people. The difference was only in the methods.'
After President de Klerk's historic speech one Friday in February 1990, unbanning the African National Congress (ANC) and announcing the imminent end of apartheid legislation, Mr van
der Merwe realised there was no turning back.
'We'd thought until Red Friday that we could keep the Group Areas and we could negotiate for partition,' he said. 'But now I realised this was the end of an order and the beginning of a new order. What Afrikaner people have to do is realise the inevitability of the new order and devise a new strategy to reach our aims.' This, he feels, the National Party has done. So where does he differ from them?
'Not much. We're Afrikaner nationalists. They have a more cosmopolitan image. The NP cannot be seen to care especially for Afrikaners. But in their heart of hearts they remain Afrikaners and that is where they are politically. They favour the Afrikaner.'
And the right wing? What is its future, following the recent defection leftwards of five more Conservative MPs? 'The right wing consists of 130 far-right outfits, but they're just study groups with half a dozen people each. The AWB (the Afrikaner Resistance Movement)? Well, after the Jani Allan business (the Terre-Blanche case), decent Afrikaners will openly distance themselves . . . They've only got circus value left. As for the CP, it's finished.
'Treurnicht is 72 and tired. The real leader is the deputy, Ferdie Hartzenberg. His political beliefs are very simple: there will again be a whites-only election and we'll win. In government, the CP will restore some apartheid laws; send back the 9 million squatters; abolish Cosatu (the trade union body) - he'll . . . send Mandela back to jail and ban the ANC again; ignore the international community; sweat out the economy - and voila, that's it]'
So what is the answer to South Africa's problems? 'It lies in the magic word 'regionalism' - which means federalism but we don't use that word because the ANC doesn't like it.
'If you cut the country up into 10 regions - Natal for the Zulus, the south-east for the Xhosas, the north-western Cape for the Afrikaners, and so on - you defuse the power struggle, you reduce the pressure levels. Each region should have its own police, legal system, executive and fiscal authority. Maximum devolution. Like the United States.'