Force will have the usual meaning of force meaning physical force. This would include I think any deliberate ignoring/trampling over an express wish of the land owner. I will double check this answer later today but I am pretty sure that this is correct.
I still find some ambiguity.
I still find some ambiguity. One scenario can be when the land owner tries to stand in the way of the user and the user restrains the landowner or removes him by force. Another scenario can be when the land owner warns the user verbally not to continue the use and the user persists in doing the usage against the will of the landowner. No actual physical force is used. Could you please comment.
The "not by force" requirement drives from an old authority (Eaton v Swansea Waterworks Co (1851 17 QB 267). It's meaning has been clarified and updated. If force or the threat of force is used by the dominant owner of land in order to use the subservient land then that will not be use as of right and can not be relied upon to claim an easement as of right. If the dominant use is constantly faced with complaints about the use of his land yet continues then that can be deemed to be forcible and can not be relied upon fro prescription. Cases in 2002 (Smith v Brudenell-Bruce  2P & CR 51 and 2003 (Dennis v MoD 2003 2 EGLR 121) held that the writing of 2 letters objecting to the dominant owner's use was sufficient to render continued use a matter of force. Many land lawyers take the view that any vigorous objection which is overridden by the dominant owner will be sufficient to count as forcible use.