The only CARLEN registration in 1845 in England and Wales on FreeBMD is a
John William CARLEN, reg Shoreditch Jun qr, Vol 2 p403
I think this is the baptism for that baby:
18 April, 1845 at St John Hoxton, Hackney
John William CARLENParents: John Carlen, cashier, Susan Carlen residing at Britannia St
I have not read all of the other thread but this John William CARLEN would seem to be the father of Henry Tatton CARLEN found in US. This John William CARLEN also went to the US but was still in London in 1861 with his parents, and 1871 with his wife and children. (Image shows that the surname may have been CARLEN)
4 Sebbon St, Islington
John Carlin 72, 'town traveller', b South Shields
Susannah Carlin 60, b Hampstead, Middlesex
John W Carlin 16, b Hoxton
Sarah Whitaker 28, servant
This couple were married in 1843. His occupation is given as 'accountant' and both were living in Cromwell Rd (presumably in Lambeth as that's where the marriage took place). If her age is correct she was 46 when her baby was born.
The Thomas we are looking for seems to fit the 1851 census details put up by Neil and Cando, however his parents are given as
Thomas and Susan.

Could the names have been a mistake on the part of the enumerator?

Judith