The frame is clearly not a "brand" model but either a cheap alloy unbranded job, many small stores sourced such frames to sell for £50 to £100, or a frame made by someone with basic knowledge for someone.
The welds and geometry remind me of cheap unbranded alloy frames of the 90's. later, for slightly more money frames similar to late 90's early 2000 alloy Marin were also available, an old Taiwan bicycle source book from the likes of Taiwan Bicycle Group may give some pointers. Many shops and privateers source frames and components from these guys.