step up footing from existing foundation

[LAB]

Hi all
Digging foundation for single floor extension, originall footing of 1950s house is 54cm (21ins) from DPC to the top of a 150mm (6ins) concrete base, total of 69cm (27ins) was going to carry on to achieve the same depth but found the ground hard/solid after digging about 45cm, (18ins) is there any way that the BI will allow the footing to be stepped up with the "rule of thumb" formula say 30cm (1 foot) or should I be happy with the depth, I could call him out for advice but I would be glad of some past experiences. thank you.

[welsh brickie]

that will be upto the building inspector no one else.In my experience you need to dig down to the original foundation.But call him out he might say ok.