Last October, Christine and I decided to do a mini RBRR in Ruby, our 1963 Herald 1200 Saloon, over a distance of some 225 miles. During one section about half way round we got held up in a long queue of traffic edging forward very slowly for a considerable period of time - stop/start, you now the kind of thing. Following that Christine (who was driving at the time) said the brakes didn't feel "quite right". Then as we approached a T-junction to a major A-road we had complete brake failure. Christine had the presence of mind to use the handbrake and we slewed across to the centre of the road, where there happened to be a filter lane, where we stopped. Thankfully there was no traffic coming from the right just as we slid across, nor did we travel across into the traffic travelling in the other direction.
We managed to get the car off the road and my first thought was to look in the brake reservoir, but this was full. (I checked the other one too just to make sure I wasn't looking at the clutch fluid!! My mind was a bit frazzled at the time!) So I was perplexed.
We got Ruby home and put her in the garage and there she has stayed all over the winter and spring. I've now checked again and the reservoir is definitely full. I checked the brakes and they seemed fine so I took her out for a careful road test (there's little traffic where we live) and the brakes functioned perfectly well. (Just to say, she fired up first time of asking having been sat idle for 7 months.)
So... Question: What might have happened on that day last October? What should I be looking for by way of necessary repairs?
Any thoughts, advice, help appreciated.