They (their DLM) are running you on Interleaved and on that BTw caps the Upload to 888 Kbps for some reason.
If, and when, it switches you to Fast Path you would get 1.2 Meg. Unlike other ISPs I don't think you can choose; it's all done auto by the DLM.
Nowt to do with BrightBox.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC