Saveasfilename...auto-generated..look into sheet at given cell..

There is a macro I run every week. It uses a template, fills it in with new data, and I want it to then save this new data as a new document under the heading GaS UK wk no x. x this week being week 1, next week, wk 2, and so on.

I believe the code is smth like this:
ActiveWorkbook.SaveAs Filename:=GaS%20UK%20wk + week_no + .xls",

Somewhere in the macro I will have to define what week_no is.
I could do it by having it as reading week_no = cell F5

How would I go about doing that in code, and where would I put it. Presumably the code goes above the ActiveWorkbook.SaveAs Filename..comand

(Another way it could be done is by somehow translating the date I enter into the macro itself.

At the very top there's

day_date1 = Day.Value + "/" + Month.Value + "/" +YearFigure.Value

desired_path = Day.Value + Month.Value + YearFigure.Value

I suppose I could somehow translate that into a week number which could be used to save the file name...???)

Whichever is easier, help is much appreciated!