Virgin Media webmail would require using the search field to locate the emails before moving them to the Trash folder. However be aware that the search only occurs in the selected folder and the full result set may not be displayed, i.e. scroll to the bottom of the result list to show more.
Use of an email client (like Thunderbird) would allow you to complete the task in a straight forward manner, i.e. search across all folder and then delete all matching results.