What type of seatbelts do I require in the front seats by law?
buggy is built on a 1961 chassis, can I get away with just having lap belts?
I know they are not as safe etc, but just wanted to know what my option are

On a 1961 chassis you can get away with no seat belts or indeed just lap belts. If you do fit lap belts it is compulsory that you use them. 3 point belts did not become compulsory until 1967 when it also became necessary to retro fit them to cars produced from Oct 1964. If you have no seat belts or only lap belts you will not be able to carry children under 3 years old and children between 3 & 13 must sit in the back (even if there are no belts in the back). Having said all that, for safety reasons If you can fit 3 point belts, ie you have a roll bar I would fit the 3 point belts.

I'd rather be safe than sorry and go for 3/4 point harness's, colour coded of course to the buggy..........
........or 3 point old style or standard modern.

What Merscury says^^^

Mine's a '59 base and I run without belts, safer that lap belts IMHO.

By law, all newly fitted seatbelts should be inertia, lap and diaganal, one hand fastening type so technically, most full harness installations are illegal. It's a good job MOT testers and coppers know  very little about Construction & Use regulations...