Hi Tilley, welcome to the forum - sorry your first post is a distress call!
As a general rule of thumb consider the following:
lack of power below 2,500 (ish) rpm can be EGR related.
lack of power above 2,500 (ish) rpm can be MAF related.
Given the symptoms your displaying and the age of your vehicle (8 ish years old) I would think the car is likely to still be on its first battery, unless you've seen evidence in history etc to show different, so I think your battery may be dying. Somewhere like Halfords will usually check this for you for free - so worth getting checked.
These cars have pretty complex and Italian wiring in them and it is well documented that failing batteries can produce utterly batty problems.
I'm not saying replace the battery - but definitely get it checked out.
1999 156 1.8TS Sport Pack 3
2001 166 3.0 V6 24V Super
2003 156 GTA 3.2 V6 24V
2005 156 1.9 JTDM-Jet Sport
2008 159 1.9 JTDM Lusso
1997 GTV 2.0TS Lusso
2001 147 1.6TS Lusso