This cache has been on my to do list for a very, very long time! When I first came across it I qualified but was reliant on a line of nine caches found after 1st April 2009 (see my web page http://www.15ddv.me.uk/geo/chal/terrain_difficulty_challenges.html#gridlocked_capital_style should you be interested what they were). However, on the day I actually found the cache I was only one cache (that pesky D1.0 / T4,5) short of completing the grid for the third time.
My difficulty is that I seldom go to London. However, I was up for the day with my non-geocaching partner who is a good lass and will generally let me grab a nearby cache, provided I do not take all day over it (and this was as fast a cache 'n' dash as you could wish for). So after walking up Regent Street and then along Oxford Street, admiring the lights and failing to find any presents for those awkward to buy for friends, I was able to negotiate a short detour before we set off for home.