TominScotland – You make a good point.
Security and passport checks are a complex issue for rail firms. And nobody can tell what the passport/security situation will be like in a few years’ time.
But *if* the service were to start now then the checks would either be carried out in Germany or when the ICE reaches Lille (as happens now with the Eurostar services running from Lyon/Marseilles) to London. (Eurostar passengers travelling from Brussels/Paris are checked before the train departs).
Channel Tunnel rules specify that all passengers be security checked *before* the train enters the Tunnel.
DB needed approval from the Channel Tunnel authorities for its ICE trains to use the Tunnel. It took years before that approval was granted.
But DB’s initial plans did force incumbent Eurostar to modernise its fleets with the same Siemens trains which DB had planned to, and could still, operate.