Rosie, I'm a semi frequent visitor to the Sikh temple on shawbury road, however the temple is only open twice a week and only serves langar once. For a good idea/experience of a Sikh temple and langar I would go with hails suggestion and visit a Sikh temple in southall. There is a relatively new one on Havelock road. It's a beautiful temple/gurudwara and langar is served throughout. I am happy to talk you through a visit If you'd like!