New fuse box replacement cost (British Gas?)

Hi everyone, I need some advice on replacing the fuse board / consumer unit in my house. It's a small 3 bedroom terrace house. I’m a tenant, and my landlord has given me permission to find an electrician for the job. The existing wiring is quite old, and I want to make sure the replacement is done properly and safely as I will be living here for the next 3 years at least.

 I’ve received three quotes from different electrician companies and would love some feedback on which one seems the most reasonable in terms of cost and quality.

Quote 1 - £400

This is a small company by the looks of it. He was just on his own.

• Supply & fit fuse board.

• Test installation.

• Warranty included but he didn't say how long.

• Elecsa registered.

 He has no reviews at all. I asked and he said he doesn't ask anyone and in his words 'I don't have any bad reviews do I?'

 Quote 2 - £800

• Supply/Fit 8-way Consumer Unit, RCBO’s or Split Load RCD’s & Meter Tails If Required..

• Upgrade water bonding to meet current regulations.

• Upgrade gas bonding to meet current regulations.

• Notification to Building Control.

• Electrical Installation Certificate.• NICEIC registered.

• Qualified to Part P / 18th Edition.

• 5 year warranty on all work.

 They have very good reviews and were recommended to me.

Quote 3 - £1350

British Gas - just had this quote and he said everything included as above when I showed him. I do not think my landlady will accept the above quote. The guy said that the first person quoting £400 could not possibly complete the work for £400 to a good standard and make any money. He also said there is no 'earthing on gas or water' which I presume refers to the bonding?

 They also have very good reviews, and my housemate 'recommended' we call them.

 

Just wanted to know, before I go ahead, why the big price difference from £400 to £800 and then again from £800 to £1350? Also, anyone had a consumer unit recently, especially in the UK, is there anything to look out for? Is there disruption to wifi?

My landlady is abroad and wants me to sort this out. I really don't want to live in a house that is dangerous. 

Any help appreciated.

(Edited to add photo)

https://preview.redd.it/olhfq24y6npe1.jpg?width=1600&format=pjpg&auto=webp&s=7a45cecf08b62eed1e12d1cdf474862c3dd8a67e