If you walk round to the Barbican in the evening, you cannot miss seeing tombstone-jumpers in dripping wetsuits, with shivering but admiring little brothers in tow, and often surrounded by doting teenage girls!! That is youff for you ... the picture below gives a better idea of the height of the jump ... taken at maximum zoom too - gulp!!
Of course there are rocks below which have to be avoided (adds to the fun perhaps?) - one hopes that they only jump at times when the tide is at its highest!