The market-seller has a heavy 'cockney' accent, which marks him as being from London's working class. This accent is very commonly found around London's market-stalls, as people shout from different directions trying to promote their products. The seller is using expressions that are used every day to attract peoples' attention at markets, such as speaking directly to a possible customer and suggesting something she could have for her tea (dinner). The humour, which attracts the listener's attention, comes from the fact that he is trying to sell fois gras and caviar in the same way as he would sell apples and oranges. This suggests that they are very commonplace, or could be if Britain as a whole saved a billion pounds by switching their insurance to Barclays.