The site was closed on Thursday as a mark of respect, and around half the usual workforce came in Friday.
Mr Singh, 21, from Slough, remains at Charing Cross hospital where
his condition remains serious. He and his family are being supported by Laing O'Rourke.
Counselling services have been made available to all T5 workers.
T5 managing director Tony Douglas said: 'My thoughts are with the families and friends of Mathew and Parminder, and I wish Parminder a full recovery. I am profoundly saddened that a life has been lost in the construction of T5.
'I am determined to find the exact cause of the accident and T5 will do everything possible to help the Health and Safety Executive in its investigation.'