UPDATE: two minutes' delay on the Bakerloo Line to Waterloo from Edgware Road and then four minutes' delay on the connecting train to Hampton Court. £10 (since the first delay doesn't count as I didn't miss the connection because of it.)
In reverse chronological order, just to confuse you.
Train into Waterloo delayed by three minutes. A further two minutes on the connecting Bakerloo Line. Seven minute delay against original arrival time in total.
Last night, a two-minute delay on the District Line to Wimbledon would have caused me to miss my connecting train, though that was happily delayed too. Arrived home seven minutes late.
7 + 7 =14 minutes, which is equivalent to £35. Ta muchly.
EXCITING NEWS: on Thursday, NFC payments go live on TfL buses. If you see someone smugly tapping their mobile phone against a reader, rather than an Oyster card, it could be Signal Failure. I pity all you technology have-nots.
Oh, and London's black cabs are to offer you free WiFi, as has been reported by nearly everyone and in a variety of languages. Just do a news search: I can't be bothered to pick a link, nor to use the likely ad-riddled service which would in any case make me feel travel sick.