Look me up next time you're in London.

[Saneta]

1.Look me up next time you're in London.

2.Look me up next time you will be in London.- why not?

thanks

[Dozy]

This is essentially the same rule that says we don't use the future tense with time references like "when", "until", "before", etc.

"Look me up when you're in London."
"Don't call me until you reach London."
"Call me before you reach London."
etc.