Hi Chelle
It would most probably help the councils and funeral directors if you had the exact date (or near enough) of death for your grandfather and grandmother.
Although the Watford site is currently out of action, there is information at the Hertfordshire site here
http://www.hertsdirect.org/atozofservices/distborserv/burialgrave/Although Vicarage Road may now be closed for new burials, it may still be possible for burials in existing plots if they were purchased for multiple use.
You may be able to speak to someone at Three Rivers cemetery dept here, cemeteries are usually open on bank holidays and some of the staff may be available to help
http://www.threerivers.gov.uk/Default.aspx/Web/CemeteriesAlthough they lived in Watford, don't exclude the possibility of burial just outside eg Carpenders Park
http://www.brent.gov.uk/cemetery.nsf/Cemeteries/LBB-8or Harrow Weald
http://www.harrow.gov.uk/site/scripts/documents_info.php?documentID=481&pageNumber=3or North Watford Cemetery
http://www.yell.com/b/North+Watford+Cemetery-Crematoria+and+Cemeteries-Watford-WD250AW-452149/index.htmlAnd just to clarify, Breakespeare crematorium is just a crematorium, there are no burial plots except for ashes.
Although most Funeral Directors will take out of hours phone calls, unless you track down the one that was used last time, they won't be able to help until they speak to the cemeteries dept when they re-open on Tuesday.
You may also have to come to terms with the possibilty of not being allowed a burial in the same plot if it is full. To overcome this most cemeteries allow the interment of ashes after cremation.
Chelle, please don't worry about the time it takes to find the plot, both Watford & Harrow Councils cemetery departments deal with this type of enquiry almost daily. And the Funeral Director should also allow the family plenty of time to make all the necessary arrangements and give you all the options.
I hope this is helpful for you at this time.
Dawn