In the third Doctor story, where exactly the same thing happened... The Doctor was off planet when it started. All UNIT had done was evacuate London and shoot up the place.
In a mirror universe audio story where the 3rd Doctor was someone else (David Warner) who landed post-trial in Hong Kong 1999, rather than Great Britain 1970, a brief account of a Doctorless 20th century informed us that UNIT's final solution to the Dinosaur question was nuking London.
In a mirror universe audio story where the 3rd Doctor was someone else (David Warner) who landed post-trial in Hong Kong 1999, rather than Great Britain 1970, a brief account of a Doctorless 20th century informed us that UNIT's final solution to the Dinosaur question was nuking London.