uk visitors visa

[chintulu]

hi, i have an appointment with uk embassy for uk visitors visa in the end of may,do they stamp the visa on the same day ? or do they post my passport later ? is it better to buy the ticket now, or to wait till i get the visa, as the ticket fares are really high now....
please help,
tahnks

[peace]

Please post in the uk section.
This is the US section.