To add a nutritional aspect to the previous answer regarding the salt:
In 2003, Scientific Advisory Committee on Nutrition published a report, where they concluded, that there is a strong link between high salt intake and high blood pressure. It was also concluded, that salt intake in British population is dangerously high and the action is required to reduce it.
As a result, salt reduction was made one of the public health priorities by the Food Standard Agency. Food Industry was encouraged to reduce salt content voluntarily in over 80 food categories. The companies, that agreed to support this programme included Costa, KFC, MacDonald's, Pizza Hut and others. These companies reduced amount of salt in their products according to guidelines. To find more about this initiative, check out the FSA report.
So, not going into further details, the reason your food is not salty enough might be because this particular restaurant aims to adhere to these guidelines. Therefore, the decision to add or not to add salt is entirely up to the consumer. Feel free to add salt, just try not to exceed daily requirements of 6 g a day! :)