Pallot's Baptism index 1780-1837 once contained about 12 million records. Unfortunately it was bombed during World War II and all that survived is about 200,000 records which makes it a substantially smaller index covering at least partially in the London area, only about 22 parishes.
If George consistently gave his birthplace as Lambeth Surrey then unless there is any reason to suspect he would have been baptised at St Pancras Middlesex across the Thames you might expect to search for his baptism in the Lambeth area (bearing in mind the IGI is a very imperfect index and has far from a 100% coverage of parish registers). There are baptisms on the IGI for St Mary's Lambeth with a father Richard Harding but not for a baptism for a son George. The IGI has indexed the Bishops Transcripts from St Mary Lambeth and not the registers themselves so it might be worth checking St Mary Lambeth actual registers at the LMA for George's baptism, as Bishops Transcripts (the yearly copy of registers sent to the Bishop) often have mistakes or missing years.
RICHARD HARDING
Christening: 25 OCT 1807 Saint Mary, Lambeth, Surrey
Father: RICHARD HARDING
Mother: MARGARETT
ELIZA HARDING
Christening: 28 JUL 1816 Saint Mary, Lambeth, Surrey
Father: RICHARD HARDING
Mother: MARGARET
There are two others slightly later for a Richard Harding with wife Frances. The baptism entries in the register will give the father's occupation.
Regards
Valda