The amount of milk in the bottle varies between shots when Lee starts drinking it.
Wendy lists her date of birth in 1945 instead of 1947, she also mentions she was turning 30 and unmarried. This would be in 1975.
Lucy turned 30 in the episode Party set in 2009 giving her birth year 1979.
Tim though is ten years older than Lucy, born in 1969 - 6 years prior to meeting their father.
The date of this episode is in 2024 (giving the time jump and Pub Quiz being set in that year). That makes Wendy 79. Geoffrey is quoted in Murder at Christmas as being 20 years older than her. Taking into account the 2 year difference, he would now be 97.