conveyancing question...

[fido]

...for the legal types.

i'm completing next week on a house purchase, and the solicitor has asked for a bankers draft on the day before completion.

two questions: i. wouldn't electronic transfer (e.g. CHAPS) be easier (it's a large sum) and ensure immediate transfer of cleared funds? ii. why the day before completion? (someone may have explained this to me before but i've forgotten)

the exchange was rushed a little bit (due to my buyer's delaying me by at least two weeks) and my mind is worrying about very litle detail...