I bought my car second hand and don't know when it was last serviced. Car has done over 100,000 miles, it's a 2004 Corsa. It's due for its MOT, so I was thinking of doing them at the same time. Also, not sure whether to go for full service or interim one. Any ideas?
The short answer is: maybe.
Most shops will offer some sort of inspection service, recommending items of concern or things that should be fixed right now. This is usually a for-pay diagnostic process. Depending on the shop, they may have a fixed price that covers the diagnostics and some low-cost maintenance items.
For example, if you don't know when the oil was changed, they'd almost certainly recommend new oil.
Keep in mind, this is the 21st century and the shop (especially if they are a dealer) might be able to look up more history than you expect. For example, my Subaru dealer has access to all the Subaru-performed service that has been performed on my Subarus since we bought them. Since I used their website for a lot of my own service records, there's more on there than you might expect.
Yes - go for a full service - a car with an unknown history should be serviced to a: gain a little insight into the state of the engine and car and b: give you (the new owner) a bit of reassurance that the car wont break due to a small issue and that it will function as it should.
Some garages do provide inspection services but I would suggest that given the car has done 100k miles and you dont know when the timing belt was changed that you get it changed as a matter of course - I didn't and had one let go on me resulting in a new engine for the car.
If in doubt, full service. I was in the same position as you, Donna, very recently. There was a full service history, but it wasn't itemised - so I had no idea what was actually done apart from giving an educated guess based on bills.
In the end, I went for a full service - oil, oil filter, air filter, sparks, gearbox oil, brake fluid, pads and rotors (they were horribly rusted, so consider this an extra in my case). Ask the dealer for the price of the parts, as you might be able to buy aftermarket parts cheaper online and provide them to the mechanic - I did that with my oil filter, air filter, pads, and sparks. This is, of course, assuming that the mechanic will accept parts.