Hello Rosy,
I also have been trying to trace London Leleux. My great grandfather, Charles Leon Leleux, was born in Hammersmith 12 April 1857, the oldest of 8 children of Augustus Peter Joseph Leleux, machinist, who was apparently born in Paris France around 1825, and Julia Piguet. I have a lot of miscellaneous information about APJL; he lived in a host of places around Holborn and Westminster, and finally died in Woolwich 1893. But I have always been curious about when/why he came over to England, and about his relationship with the Lambeth Leleux, who appear in various documents around the same time, and lived just over the bridge on the South Bank. It doesn't seem to be a Huguenot thing - I suspect both were later immigrants.
I have come across Joseph Leonard Leleux, who married Eliza Bigg of Bethnal Green, on 21st June 1832 in Hackney, per Vicar-General's Office document, but I thought that she was actually born in Shaftesbury, Dorset (per 1881 Census). The children I am aware of are Alexander Leonard (b Feb 1834 Kennington), Eliza May (b 4 Sep 1838, Lambeth), and Florence Adelaide (christened 23 Jan 1847); I also tentatively had Julius Lovell (b 23 Jan 1836) as one of their children. I assume you are descended from one or other of these.
However, I'm afraid I have come across no further information about Joseph Leonard Leleux.
My brick wall is Augustus Peter Joseph Leleux - whose father was apparently Louis Leleux, farmer, from France. My brother & I incline to the theory that they came from the Ardennes/ Champagne area of France, but no hard facts. We suspect that APJL was related to JLL - if only because the London Huguenot Leleu-s rarely if ever had "X" at the end of their name - but have found no way so far of establishing that.
I'd be very interested to see if you have any insights from "your" side of the river.
Best wishes - John Humphrey