He works in civil defence; can he do Hajj in his work clothes?

Praise be to Allah.

There is nothing wrong with you doing Hajj in your military clothing and you are obliged to do the actions of Hajj, as mentioned in the question, and you cannot do your work wearing the ihram garments, because the official department does not allow that. But because of that you have to offer expiation, which is feeding six poor persons, giving each one half a saa’ of dates or rice or other local staple food, or by fasting for three days, or sacrificing a sheep in return for wearing tailored garments. You also have to offer something similar for covering your head. 

And Allah is the source of strength. May Allaah send blessings and peace upon our Prophet Muhammad and his family and companions. End quote. 

Shaykh ‘Abd al-‘Azeez ibn ‘Abd-Allaah ibn Baaz, Shaykh ‘Abd al-Razzaaq al-‘Afeefi, Shaykh ‘Abd-Allaah ibn Ghadyaan