Horton, who also won 20 caps for England, attended many of the Lions training sessions as the chief technical representative of Predator, the team’s training equipment manufacturer.
The Lions were beaten 3-0 in the Test series by the All Blacks with head coach Clive Woodward since coming in for some heavy criticism.
Horton said: “The system was designed to give each coach equal time with the players. That meant Andy Robinson had only 20 minutes to spend on scrums, line-outs, rucking and mauling.
“That’s pathetic for a side hoping to compete against the All Blacks, especially when the Lions needed to take the game to them up front.”
Horton was also scathing of the number of practice scrums in training and the side’s approach to the line-out.
He said: “In South Africa in 1997 I told Fran Cotton that the Lions needed to spend more time scrummaging before the first Test and Jim Telfer gave them a two-hour beasting - that’s close to 100 scrums.
“The maximum they put down in New Zealand was 16. Not one of the them was opposed - and they didn’t practice a single back-row move.”
He added: “Schoolboys know you don’t throw to the back in gale-force conditions. Schoolboys also know you keep it tight against the wind and kick with it, yet the Lions did neither.”