Quite difficult to trace where the power is being drawn but your best start point will be with an ammeter (10 amp min)
With ignition off, all doors shut and all lamps out it will normally draw around 0.2 amps. If the ignition has been switched on then off it will be around 0.8 amps for around 4 minutes as it keeps the engine ECU powered incase it needs to run the engine bay fan, then should drop back to around 0.2 amps.
If you disconnect the negative battery terminal and place your ammeter in series between the negative post on the battery and the disconnected negative battery terminal you will obviously get an amperage reading due to your high loss.
Using the attached power distribution circuits pull the fuses one by one starting at the under bonnet fuse box and progress to the drivers footwell fuses until you see a lower amp reading, the issue will be somewhere in that circuit. Once you have found the fuse which is drawing current the see what it feeds on the circuit diagram.
If you need a full set of wiring diagrams for your TF then send me a PM and I will email you a set in PDF
I know it's not the solution, but for the interim you could fit a battery saver connector and just switch it off overnight to save disconnecting the battery to prevent it going flat.
I have one fitted just for convenience as per the image below.
Let us know how you get on.
Brian.