Jan you need to go and find out the difference between tower control and radar. Once tower is responsable for seperation the rules change.
http://www.caa.co.uk/docs/64/2008901...ficationV3.pdf
Here is the UK airspace classes VFR isn't seperated from VFR in class C.
And Vizsal there is no requiment for an instructor to be in the tower or have a hand held in the UK or for that matter to watch.
And to be honest why an instructor should take control away from a trained ATCO who has been trained for over two years to stop aircraft hitting each other I don't know certainly wasn't covered in my FIC.
Also having two people giving instructions on frequency is just going to add to the confusion.
I also suspect its illegal and you would be setting yourself up for a manslaughter charge if there was an accident.
Another point for students is that if your not feeling confident or want max protection don't tell a controller that your visual with anything. If you do that they have to visually seperate you from the tower and "control" you to deconflict. As soon as you declare visual the onus then comes to you to remain seperated. (Which is what Jan needs to read about)
And another report to make you think
http://www.aaib.gov.uk/cms_resources...LZ%2012-10.pdf