Here is a guide on how to flash a FTF (official firmware) to the Xperia Play using Flashtool. You do not need to have a modified or unlocked phone for this to work for you.

Flashing the FTF

1. Download and install the Flashtool package and download and extract the R800i_4.0.2.A.0.58_Enhanced.zip.
2. Next go to where you installed flashtool and then to the drivers folder.
3. Run the Flashtool-drivers.exe file.
4. select “your drivers”, flashmode and fastboot drivers.
   

   

5. Accept all the prompts and once finished load flashtool
   

   

6. Now select flashmode and click the “…” button
   

   

7. Select your FTF file from the left side and keep “exclude kernel” checked then press “OK”
   

   

8. Switch your phone off and press and hold the back button while connecting usb lead (Green LED)
9. It should start flashing and once done will say “Complete”, Reboot and your done.

Congratulations you have now successfully flashed a FTF file using flashtool.