If I create a new project it works fine.
BUT when using old projects changing the tempo, midi parts behave like audio parts i.e. they don’t follow bar and beat information → i.e. dont change speed
If I get Groove agent to “follow tempo” it does but the midi parts don’t
any ideas? - I cant see anyone else reporting this problem - which fills me with horror
you can switch Time between musical and linear for each track. On your audio track it’s the orange button with the note symbol, indicating that currently that track is in musical mode, following the tempo of the project.
The same button exists for the Midi and Instrument Tracks (but you currently don’t have them displayed). You can click the cogwheel at the bottom right of the track list, and add toggle time base to the display.
will look - didn’t know you could do that with midi track (obviously) knew that about audio - thanks for the response
oh my goodness - been using cubase since the start and I have never done that with midi tracks = clearly I must have done it accidentally and then copied the track or something
Brilliant - has caused me a morning of pulling my hair out - thanks again (stupid me)
I would love to hear Mr. @raino add some words here 
@alexis Your wish is my command.
All Tracks can switch between Linear & Musical Timebase. When you place an object (Events or Parts) on the timeline the Timebase setting determines if the object’s starting position is anchored to minutes & seconds (Linear) or bars & beats (musical). And that’s all it really does.
Musical Mode only effects Audio Events. When it is enabled the Length of the Audio will be different at different Tempos - at slower Tempos the Length expands and at faster Tempos it contracts - but the length of the Event is always the same when measured in Bars & Beats. When Musical Mode is disabled the length of the Audio Event remains constant when measured in minutes & seconds but will change with different Tempos when measured in bars & beats.
MIDI Parts do not have a Musical Mode setting. They always behave the same as an Audio Event with Musical Mode enabled - i.e. they maintain a constant length when measured in bars & beats.
Except Tracks don’t have a Mode setting, only a Timebase setting - which is what you are referring to.
I wish Steinberg had named things so they weren’t so easy to confuse with each other. It really creates a lot misunderstanding around this whole topic.