Sh. Amit Batham ji,
(i) It appears that High Court Order is silent on the issue of interest. The issue of interest should have been raised before the High Court. Has your client not filed writ petition for recovery of GST along with interest ?
(ii) Govt. (PWD department) is the defaulter. The service supplier must not suffer because of the fault of the recipient of the service. Whether service receiver is Govt. or private firm both are at par in the eyes of GST laws.
(iii) As per Section 2 (84) (k) Central Govt. also falls in the definition of 'person'. Both are 'persons'. Hence Govt. is not above law. There is no separate yardstick for Govt. department.
(iv) To recover interest from Govt. department is a hard nut to crack. It does not mean your client should become dormant or surrender meekly.
(v) In terms of Section 9(1) of CGST it is a statutory responsibility of the service supplier to collect GST from the recipient of the service and deposit with Govt.
(vi) Interest is an integral part of tax. So your client can legally collect /recover interest from Govt. Department.
(vii) Your client should again approach High Court for rectification of the Order for recovery of interest from Govt. department (Service Recipient).
(viii) If you do not fight legally for your right, you are defeated today itself.
There is no other route except High Court for recovery of interest.
Disclaimer : These are my personal views for education purpose only.