Obeyesekere, J

1) There are two issues that arise for determination in this appeal. The first is whether the Plaintiffs – Appellants [the Plaintiffs] have proved that a sum of Rs. 68m they claim was due to them from the 4^th Defendant – Respondent [the 4^th Defendant] has been remitied by the 4th Defendant to the 1st – 3rd Defendants – Respondents [the Defendants/KKH]. The second is, if so, whether the Defendants have been unjustly enriched by their refusal to pay the Plaintiffs a sum of Rs. 55m out of the said sum of money.

Background to the appeal

2) The Plaintiffs filed action in the High Court of the Western Province holden in Colombo exercising commercial jurisdiction [the Commercial High Court/the High Court] on 6^th June 2006 against the Defendants under eight causes of ac alternative 8th cause of action. The Ceylon Electricity Board had been named as the 4th Defendant only for the purpose of notice and no relief had been claimed against the 4^th Defendant.

3) Pursuant to the answer of the Defendants being filed, an objection had been taken with regard to the maintainability of the 1^st and 2^nd causes of ac the parties had agreed in terms of the contracts that existed between them to refer any disputes that may arise in terms of such contracts for resolution by arbitration. The Plaintiffs did not resist this objection and had informed the High Court that it will not be pursuing the 1^st and 2^nd causes of ac

4) The Defendants had also raised an objection that the 3rd, 4th and 5th causes of action are prescribed. Having heard the parties, this objection had been upheld by the High Court by its order delivered on 4^th March 2009 and those three causes of ac been dismissed.

5) The case proceeded to trial thereatier with only the 6th, 7th and 8th causes of action [together with the alternative 8th cause of action] remaining to be decided. While the 2nd Plaintiff gave evidence on behalf of the Plaintiffs, the Defendants did not lead any evidence. By its judgment delivered on 3^rd August 2018, the High Court held that the 6th and 7th causes of action too are prescribed, and that the Plaintiffs have failed to establish the 8th cause of action and the alternative 8th cause of action.

6) Aggrieved by the said judgment, the Plaintiffs filed this appeal. At the hearing, the learned President’s Counsel for the Plaintiffs submitied that he would be limiting his submissions to the rejection of the 8th cause of action that alleged that the Defendants had been unjustly enriched in a sum of Rs. 55m, and the alternative 8th cause of action.

The parties and their contractual relationship

7) The Plaintiffs are carrying on business in partnership under the name, style and firm of CA & Company, primarily as civil engineering contractors and hirers of earth moving vehicles. The Plaintiffs also provide manpower, raw materials, construction machinery etc., to foreign companies that are engaged in construction projects in Sri Lanka.

8) The Defendants are public companies incorporated in Japan and are engaged in the business of civil engineering and construction projects. The Defendants had formed a joint venture partnership under the name and style of Kajima Kumagai Hazama [KKH] in order to bid for and engage in large scale civil engineering projects in Sri Lanka.

9) In 1999, the Government of Sri Lanka had approved the construction of a hydro power station at Kukule Ganga. Pursuant to the calling of tenders, the 4th Defendant had awarded to KKH the contract for the construction of the dam. KKH had selected the Plaintiffs as a sub-contractor for the supply of aggregates and quarry sand, earth works on the head pond areas and excavation and other preliminary works, and entered into three contracts with the Plaintiffs in August 1999 for the provision of the above services. These contracts provided that any dispute among the parties arising under the said contracts shall be resolved by arbitration. The aforementioned 1st and 2nd causes of action had arisen under these