I have not found this function,

But you can update progress on daily or even hourly basis,and MSP will keep all this record.
e.g. for a task, you input actual data as follow:

day 1 8 manhour
day 2 6 manhour
day 3 7 manhour
day 4 9 manhour

anytime you open task usage view or other resource view, you can see these data

Also thankyou from me!
I will be attempting to set up a system where-by my sites update a spreadsheet with dates and % Work Complete, and I can then import this in every fortnight.

You have different ways to exchange information between MSP and other application.
· Create a dynamic connection between the information in the source and target application. When one is updated in one, it’s updated in the other as well [LINK];
· Bring information in MSP from another application or another file format, making information appear as if it were created in MSP [IMPORT].

A - LINKING FROM MSP TO ANOTHER APPLICATION
Major advantage is that the file size is smaller than it would be if the info in the linked file were embedded.
Major disadvantage is that you should know the current location of the linked file and its update status. If the lined file is moved, the link is broken!
1- in MSP display view the info you want to copy/link to the other application;
2- Click Edit, Copy;
3- Open the other application (Excel, Word, etc …);
4- In the target application click Edit, Past Special;
5- In the Past Special dialog box, select the Past Link option;
6- Review the Display as Icon box
7- Good lucky.

B - IMPORTING/EXPOTING INFORMATION
Importing/Exporting essentially converts the info from the file format of the source application to that of the target one.
MSP support Access databases (mdb), excel files (xls), text file (txt), CSV files (CSV) and XML format files (XML). Information may also be exported to or imported from an ODBC database, which is a protocol used to access data in SQL databases servers. With ODBC driver installed, it is possible to connect a MSP databases to SQL databases (equivalent to the Pervasive driver for P3).

IMPORTING INFO INTO MSP
You start the import process simply using the File Open command.
1 – In MSP click File, Open;
2 - In the type list open dialog box select the format of the file you are importing;
3 – Browse, and select the file to import;
4 – Read the Import Wizard welcome page and click Next;
5 – On the Map page, select the New Map option then Next;
6 – On the Map mode, select how you want to import the data (as a new project, append the data, merge the data), then Next;
7 – In the Map Option page, under Select The Type of Data to Import, click the info you required, Task, ect… then Next;
8 – Open the Mapping page, complete the field to specify info to be imported. Specify how fields from the source application are to map specific MSP field. Any unmapped data will appear in red and will be not imported;
9 – On the End of Map Definition Page click Finish.

EXPORTING INFO FROM MSP
Open the project. Click Save As and select the location where to save the file as well as the type. If you want to export your data to a Microsoft SQL server click ODBC button.
For both solution go through the Export Wizard specifying the data you want to export.

ODBC link may be slower and for huge data base not work at all (out of time).