Would you be able to get a picture? If not, could it of been a newt?

From that very basic description it sounds as if it might be a newt. Are the potatoes in your garden or in a bag in the larder?

Also, if you care not to state what country you live in, what kind of climate do you have? After all, there are places in the world where it would be a small crocodile.

Most crocodile newly hatched babies are all over 15cm long so not 100% sure it would be, but as you said Loosestrife location would be very helpful.

Newt was my first thought too. Especially if one of your neighbours has a pond.