Cellar vole

Last week I saw a vole in the cellar while I was fixing a valve on the central heating. This afternoon I waited quietly and within a few minutes a bank vole emerged from a hole by the gas pipe. It took a few attempts to get a picture, but after vole #1 lost patience and ran into the depths of the cellar, it was quickly followed by vole #2 and ten minutes later by vole #3.

In general I like voles, especially if they lived in the woodpile left outside for their convenience, and wouldn't mind them in the cellar. However there has been some nibbling of suitcases in the loft, to say nothing of holes in an inflatable bed stored there.

So they will have to go. The problem is - how will I know if they are in or out when I block up the hole?