What a lot of do-gooding **** being spouted!
You no doubt bought the house for a number of reasons, and the parking was a feature of the house. It’s something that contributes to the value of the property and therefore contributes to the price that you had to fork out to buy it.
The land is yours, and if you want to occasionally park on it, and leave it empty for the rest of the time then you should be able to do so without hindrance.
I’m not advocating falling out with your neighbours, but if they take offence and get arsey to you nicely asking them not to park on your land, then they’re probably not the sort of people who you want to be friends/neighbourly with anyway.