I'd say redeem a J award to Delhi. These are typically hard to come by (sometimes even during the low-season) but well worth it. From there, you can take a tour or come up with your own itenrary to visit places such as Jaipur, Agra, Udaipur, Jodhpur, etc. I'm not sure what your budget might be, but if you can afford it then take the tour on the "Palace on Wheels" train. As someone mentioned earlier, you could even go to Kathmandu from there. Delhi and Bombay are also typically more expensive to fly to from London than most other cities in the region.