Most of the Bangladeshi migrants in UK migrated there in 1980s and 1990s. This is too short a period to substantially alter the height of a population, specially any person who was short in Bangladesh will not gain height just because he/she lived in UK for 30-40 years and adopted UK diet. It will at least take 3 generations. If you have any data on the average height of 3rd generation Bangladeshi, Pakistani British then share.
The effect of nutrition on Height depends on mainly during gestation and early childhood. A generation became taller when their mother and father do not suffer from malnutrition, have good health care and provide a good health care and nutritious diet to their children. It is a long process.