We are just starting to work towards my son sitting the exams next year.
St Ambrose is probably first choice but will also sit AGSB and Sale.Our tutor has suggested cem books but as St Ambrose is GL, is it better to use these or both?
Thanks in advance for any suggestions

No idea about GL as didn’t go for Alty boys. We used CGP practice books and the 10 min test books. The 10 min test books are fab. I also used Bond How to do NVR and Maths books over the summer which I wish I’d found out about earlier.
Check out other areas of the forum for GL recommendations. Your tutor should know though!

Not from your area, but there are suggestions for practice materials here https://www.elevenplusexams.co.uk/schools/regions/trafford-11-plus
Agree that your tutor should know, that's partly what you are paying for!

I found the CPG books by far the best for all subjects, if you go through the study book and practic book you can't go wrong really. Quickly cross reference against the question types info on here to check you have covered all bases. If you have a GL VR or English test to prep for you're in a great position as the actual test provider publishes tests which my DD said were super accurate and slightly harder than the real thing.