Hello Matt,
You should consider upgrading to Full Membership...
Now, that being said, I'd store my car each year, from late October/early November, until generally May of the following year, at least 6 months out of each year. Most of the time it was stored in an unheated garage in central Michigan where it gets cold, the likes of which most Brits don't understand. I did this for about 20 years. The home storage there was a home "kept open" in the winter, and on occasion if I went up there in the winter AND the roads were dry, I would take it out for a 10-15 mile "exercise". When the car was stored each autumn, it was freshly washed and with a full tank of gas, with stabilizer added. E10 10% ethanol gas. In storage I disconnect the battery by removing the ground strap. Each spring my car never failed to start although on some occasions I did need to charge the battery a bit.
I was always told that just starting and warming it up wasn't good. Run the car.
In all those years--probably about 20--my engine never failed to turn over.
While anything is possible, if your car started and warmed up recently, I can hardly believe it became "seized" during storage.
One thing to fully check is your starter motor and the cable going to it. Assume this is an issue before thinking it's the engine internals. I might say otherwise if it's been sitting for years never started with unknown conditions.