Helllo Rob and welcome
It has all the attributes of an International One Metre (IOM). Check the length including the soft bow bumper if it has one.
It has similarities to a Nimbus Mk3 which is a Graham Bantock design about 20 years old now. The transom is different though. It is a popular home build boat and there is a thread on this forum here by Eddie Lancaster called a Couple of IOM Yachts. Even if is not an IOM or a Nimbus the steps to finish it off and equip it can be very much the same.
Your sails, masts, boom and fittings are identifiable as SailsEtc products and that company is owned by Graham and Lorna Bantock. It is a great company and very helpful. If you go to their website there are lots of downloadable instruction sheets and a comprehensive catalogue. I have often sent enquiries by email to Graham and he always responds quickly and clearly.
I can't see from the photos whether you have the lead ballast? The rig looks equivalent to the middle sized No 2.
What ever it is, it's a very nice gift and worth finishing to the high standard that appears to be from the pictures.
I have two IOMs. A Topiko and a Boxkite. I am planning to build another more modern design and have some of my own ideas on the table for a fourth.
I hope it goes well.
Tim R