Okay I managed to resolve this by doing these steps on a pc:
1. download fastboot image from
http://en.miui.com/thread-4790869-1-1.html
2. unzip the downloaded file and the file inside that
3. use fastboot (volume down + power button) to run flash_all_except_storage.bat (this will install the image without wiping userdata/apps - like an upgrade)
4. go back into fastboot and install TWRP again as the stock recovery will have been installed
5. boot into recovery (volume up + power button) and install xiaomi.eu rom again
This all worked for me, now booted into 10.1.2 on my mi5s