The doctrine of the separation of powers is a fundamental principle in constitutional law where the government is divided into three branches: the legislative, the executive, and the judiciary. Each branch has distinct powers and responsibilities to prevent any one branch from gaining too much power.

In context to the question, the doctrine's practical application has been described differently in various countries:

• United Kingdom: The British Constitution does not strictly adhere to the doctrine of separation of powers. Instead, there is an overlap between functions and powers among the branches, allowing flexibility and adaptability.
• France and the U.S.A.: Both countries have tried to maintain a stricter division of powers among branches; however, complete separation has not been successful in practice.

The question asks which committee or individual has summed up this interpretation of the separation of powers doctrine. The correct answer is the Donoghmore Committee. The Donoghmore Committee emphasized the practical overlap of powers even in systems where theoretical separation is sought.

To justify why the other options are incorrect:

• Prof. Ullman: No significant reference to this doctrine in the context given.
• Prof. K.T. Shah: Not specifically known for summarizing the concept of separation of powers in the manner described.
• Wade and Phillips: Known for works on administrative law but not specifically connected to this particular summation.

Thus, the best fit for the provided statement regarding the doctrine of separation of powers is the Donoghmore Committee.