Originally Posted by star_world

Security check upon entering Flight Connections, and then you are deposited into the departures area of T1 again. No immigration or customs in the UK, both happen when you arrive in LIS.

Depending on the time of day the security line can be quite long - I would allow 90 minutes between the flights and you should make it comfortably. If it's booked together as a codeshare you'll be protected on a later flight in the event of any delays without issues.