Explaining with Big Mac Index that I wrote in the past, Big Mac costs 2.79 GBP. It deserves about 530 JPY. Instead, it takes only 360 JPY in Japan. It means that the prices in London are higher than in Japan by 1.5 times.
Japan had encountered continuous deflation for several years until Abenomics began. Therefore, it is natural to feel prices high in foreign countries. In addition, I think European people are not eager to desire low prices. In Japan, some restaurant franchises were competing to lower the prices continuously in recent years. As a result, consumers could eat cheap food with low cost. However, some companies were criticized as forcing employees to work excessively. Now, many franchises including McDonald's have to change their sales strategy in Japan.
Also in the UK, some supermarkets offer low cost foods. I usually go to Morrison's. Although most foods are expensive compared to Japan, there are some exceptions.
Rice is expensive in Japan, because the government regulates high rate of custom duties on rice to protect domestic farmers. Some brands of Japonica rices are extremely delicious, but it costs 2 GBP per kg or more.
Instead, I can get several types of rice in London, all of which are inexpensive. Pamella rice is similar to Japonica one. And Basmati rice is nice long-grain rice. I love it! Each one costs 1.1 GBP.
This is the cheapest one, only 40 pence per kg. Unfortunately, taste bad.
The UK is a nation of breads. There are large variety of breads. Most of them are good.
This is a series of plain scone by Morrison's. Only 1 GBP. Surprisingly, taste great so that any luxury breads are questioned. Try it!
(3) Cooking sauces
The UK is a nation of stew cooking. You can see enormous kinds of cooking sauces. To be honest, I do not like British stew cuisine. Some sauces taste not so spicy. You can get one with 1-2 GBP.
This is Morrison's brand curry sauce. Only 20 pence! Usual curry sauce costs 1-2 GBP in Japan. It tastes a little weak. I add chili-pepper on it.
Minced beef with curry sauce, quite delicious.
The prices is highly associated with the culture. I will investigate the differences between the UK and Japan in other regions about prices.