Postscript

Have just received the final quotation from Sytner, who have also very kindly reduced their labour rates.

The original estimate for parts, labout and VAT was;

• Gearbox - £3,700
• Injector - £470
• Glowplug control unit - £226

Giving a total of £4,396

The revised quotation is;

• Gearbox - £2027.46
• Injector - £450.13
• Glowplug control unit - £209.67

Giving a new total of £2,687.26, which is a reduction of £1,710.

It is still a massive bill and it has taken a huge amount of effort to articulate my case to BMW in order to achieve this result. 

However, I've learnt my lesson and will ensure that I don't keep a vehicle - especially a BMW, past its 5th birthday.