Thanks for your good advice Greg
Making this work on Raspbian is quite easy so I tried to find a similar route to make it work on TCL and here is what I came up with.
ABElectronics guide to Raspbian includes the following steps:
1. Enable I2C
2. Install python-smbus with 'sudo apt-get install python-smbus'
3. Install python3-smbus (I also tested it without this and it still works)
4. Install python-dev with 'sudo apt-get install python-dev'
5. Install python3-dev (I also tested it without this and it still works)
6. Install i2c-tools with 'sudo apt-get install i2c-tools'
7. Disable the lines 'blacklist spi-bcm2708' and 'blacklist i2c-bcm2708' in the raspi-blacklist.conf file (This was already done in the '2015-11-21-raspbian-jessie-lite' image I used or perhaps it was the work of raspi-config)
8. Add 'dtparam=i2c1=on' and 'dtparam=i2c_arm=on' in the config.txt file (I uncommented the lines already present)
9. Add 'i2c-dev' to /etc/modules (This was already done by the raspi-config)
10. Add the ‘pi’ user to the I2C group (This was already done by the raspi-config)
11. Download the pythin library from ABElectronics with 'git clone
https://github.com/abelectronicsuk/ABElectronics_Python_Libraries.git' (I installed git 'Sudo apt-get install git-core' and downloaded the library)
12. Add the AB Electronics python library to the PYTHONPATH with 'export PYTHONPATH=${PYTHONPATH}:~/Desktop/ABElectronics_Python_Libraries/IOPi/'
So I did the following on TCL:
1. Having checked the TCL I came to the conclusion that I2C was already enabled in the 'piCore-6.1_v7-SSH' image I used
2. I did 'tce-load -wi py-smbus' as I could not find python-smbus for TCL
3. Here I relied on 2. as I could not find a python3 version of python-smbus and it worked fine in Raspbian without it
4. I did 'tce-load -wi python-dev'
5. Here I relied on 4. as I could not find a python3 version of python-dev and it worked fine in Raspbian without it
6. tce-load -wi i2c-tools
7. Here I did nothing as I could not find these lines disabled anywhere in TCL
8. Here I did nothing as these were already present in the config.txt file
9. Here I did nothing as i2c-dev was already present in 'bootlocal.sh'
10. Here I did nothing as I have no 'pi' user nor a 'I2C' group (This is probably the reason that I need to use 'sudo' when I execute python code involving the I2C-port)
11. I installed git as you suggested 'tce-load -wi git' and downloaded the python libraries from AB Electronics 'git clone
https://github.com/abelectronicsuk/ABElectronics_Python_Libraries.git'
12. I added the pythin libraries with a command adjusted to fit the file structure on my TCL 'export PYTHONPATH=${PYTHONPATH}:~/ABElectronics_Python_Libraries/IOPi/'
I hope others can use this
Best regards
Claus