Adds details and background in paragraphs 3, 5 and analyst comment in paragraph 4

July 6 (Reuters) - Shares in easyJet EZJ.L climbed 12% on Tradegate on Monday after the British budget airline agreed in principle to a £5.5 billion ($7.34 billion) takeover proposal from U.S. investment firm Castlelake over the weekend.

EasyJet, which operates more than 350 aircraft on over 1,200 routes in 37 countries, said on Sunday it was prepared to accept Castlelake's revised offer of £6.90 apiece, potentially ending lengthy negotiations and reshaping Europe's aviation industry.

The potential take-private deal comes at a challenging time for airlines, which are grappling with sharply higher fuel prices and margin pressure linked to the Iran conflict.

JPMorgan analysts, however, raised concerns around how aviation-focused lender Castlelake and the easyJet board would meet European Union ownership requirements and agree on a control structure, with founder and controlling shareholder Stelios Haji-Ioannou's views also unclear.

EasyJet said on Sunday that Castlelake had agreed to a "best endeavours" commitment to obtain regulatory clearances and approvals.

($1 = £0.7496)