To discover Churchill's secret London,therefore,requires a guide,and there is arguably none better than Sir Martin.

1.译文:
因此,要探寻邱吉尔在伦敦的神秘足迹，需要一名向导，马丁爵士是毫无争议的合适人选。

2.句子分析:
To discover Churchill's secret London,-----主语
therefore,-----插入语
requires a guide,----谓语\宾语结构
and there is arguably none better than Sir Martin.-----并列句

3. "arguably"修饰全句.
又如:
There is currently none better than Firefox.
There is surely none better than the support they've got from a certain teenage girl.

注:
(1)马丁爵士(全名:Sir Martin Gilbert)是邱吉尔的官方传记作者.
(2)虽然邱吉尔出生在牛津附近,但他生活的绝大部分时光是在伦敦度过.
(3)相关资料:
London was a city Churchill both knew and loved. "He was a Londoner. He was a total Londoner," says Sir Martin Gilbert, Churchill's highly respected official biographer. Although Churchill was born at Blenheim Palace, the 18th-century country estate in Woodstock just outside Oxford, which belonged to his grandfather, he spent most of his life in London.

Curiously, however, as much as Londoners venerate their great war leader and prolific author, and, more generally, highlight the houses of famous people with blue plaques and places of historical interest with bronze plates, Churchill's homes and haunts in London remain largely unmarked.