I believe it will yield real benefits. In theory an agent in India is just as skilled as in the UK, so there will be absolutely no difference. However there are a couple of practical considerations.
1. People know that outsourced centres are cheaper. This in turn can lead to the assumption that the company is more interested in saving money than service. This will naturally put the individual in a less agreeable mood, making resolution of the matter more difficult.
2. An accent is a problem. Yusuf mentioned that it is understood around the world, but this simply isn't the case. On numerous occasions I have spoken to agents whos accents make it difficult to understand what they are saying. Having to ask them to repeat themselves after every sentence is frustrating and time wasting. This isn't levelled just at Indian centres, but anywhere with a strong accent. If the customer is speaking to someone with an accent they are unlikely to encounter frequently in every day life there are bound to be issues, complicated further by the limitations on the quality of a phone line.
This difficulty in communication can breed the belief that they don't understand you. Often if it is a service problem, and the answer is unfavourable one begins to question if the agent really understands what you are saying. This leads to further repetition and arguments.
So, to the question, the Indian agents are just as skilled, but unless they can speak with no notable accent then there are real world benefits to being based in the UK.