Solution
Go Fish
Blaze claims to have signalled Dudley as he was leaving to warn him of the flat tyre. Given that the path to the lake was only 100m and straight as an arrow this might have been possible, but for the fact that Constable Ken had to over a little hill.
It doesn’t matter how straight the path is, if there’s a blind rise it would be impossible to see anyone down at the lake, or for them to see you.
Blaze was lying, and we had him!