colee -- I think Rosie hit the nail on the head by asking you if you had inserted the reference numbers for the marriage.
I hope I can explain this without confusing you, as it is often easier to show someone something than explain in writing. Anyway here goes!
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To order from the General Register Office (GRO) - it is much easier for them if you can quote the reference number of the event which is given on the Civil Registration Index (ie the Register of births, marriages and deaths which commenced in July 1837).
This register is on the subscription sites such as Ancestry and Find My Past and also on a site called FreeBMD.
In this case of the marriage of John Butterworth to Ellen Tattersall search the marriages on the site of your choice (LancsBMD has the marriage year -- BUT the reference number they quote is for the LOCAL Register office at Preston and will NOT do for the GRO).
On the Civil Registration Index of marriages you will find the entry in the Registration District of Blackburn in 1918.
The details you want to complete the application form for the GRO are;
Page 1.
The type of application - birth, marriage, death -- just click the appropriate box.
Is the GRO Reference Number known --- click Yes
The Year of the event
Click Submit
Second Page;
Surname and Forename of at least the groom or the bride (or both if you wish)
Insert the Quarter of the event (in this case Q/E Dec 1818)
Insert District name --- in this case Blackburn
Insert Volume Number ---- this one is Vol 8e
Insert Page number --- ie 596
Then submit and pay.
Not giving the GRO the reference details means that someone will have to hunt through for the particular event you are requesting - which will of course cause administrative time.
Hence if you do intend ringing them you can provide the details given above -- but have a go at finding them yourself first, just for future reference so that you know where to look.
If any of this sounds like gobbledegook to you -- don't hesitate to come back! I know what I mean, but may not be putting it across very clearly.