With regards the use of "wilco" - could the pilot not state the following..........
"Climb FL50, wilco, G-ABCD"
Another point - surely "climb and report level FL 50" could be misunderstood to mean climb FL50 and report your present level? I understand that the word "your" is omitted, but still I don't like the phrase. Surely "Climb FL50 and report reaching" would be better. Yes "reaching" is listed in CAP413. Or "Climb FL50 and report maintaining" - maybe this is the best!